Turn an Excel calculator into a web app your team opens on a phone

Your workbook works. Someone types 5 numbers into the yellow cells and the answer turns up in the green one. Now the crew wants it on their phones, without Excel, without a copy of the file, and without anyone typing over a formula.

There are two ways to get there. You can have an AI rewrite the formulas as JavaScript in one HTML file and put that file at a link. Or you can hand the workbook to a builder that keeps the spreadsheet as the engine. This guide compares both, then takes the first route end to end: getting the formulas out of Excel, the prompt, what the file must not contain, the test against the sheet, and publishing it for your team. The vendors' pages and Microsoft's Excel help quoted here were read on November 6, 2026.

Which route fits your calculator

What the vendors' own pages say, read November 6, 2026 between 17:13 and 17:21 Japan time:

• Glide. Its pricing page says "Plans on GlideOS start at $25 per month. Annual plans are coming soon." Its comparison lists 0 published apps on Free, 2 on Basic, and 5 on Plus. Its Excel page answers "Which Excel features and formulas are supported?" with "Most common Excel formulas work with Glide, but advanced features such as macros, VBA scripts, or external add-ins may not behave as expected," and suggests that "in many cases it's best to handle logic inside Glide's Data Editor." The same page says "Your Excel files must be stored in OneDrive or SharePoint" and that syncing needs "a Business or Enterprise plan", a plan name its pricing page no longer lists.
• AppSheet. Google's help page on app formulas: "Your spreadsheet is a very powerful tool to run calculations. Those calculations run only when data syncs back to the spreadsheet." The pricing page lets you "test your apps with up to 10 users at no cost", and "Publisher Pro apps can be used by an unlimited number of users for $50/mo/app" with no sign-in.
• Power Apps. Microsoft's pricing page lists Power Apps Premium at "$20.00 user/month, paid yearly". Microsoft Learn (dated May 19, 2026): "Power Apps can connect only to Excel files that are stored in the cloud", and the data "must be formatted as a table". Its sharing page (dated September 17, 2026) says that if an app has premium components, "users must have a Power Apps license to use the app".
• SpreadsheetWeb. Its Hub pricing page (modified July 28, 2026) says it "runs all 505 Excel functions on every plan", that "Solver and Goal Seek recalculate the model repeatedly until they converge", and so they're not on any Hub plan. "Anyone opening an unrestricted application by URL is an anonymous user, and those are unlimited on every plan."
• SpreadsheetConverter. Its price list: Standard at "$15 charged per month", or $12.75 a month billed yearly ($153), with 4,000 populated cells per workbook. Its JavaScript page says it converts "the Excel formulas to JavaScript".
• Appizy. "In the Cloud plans, your web tool performs server-side calculations. This means that end users only see the interface and the results, while your formulas remain hidden." Its functions page (reviewed May 4, 2025): "Appizy uses the open-source library Formula.js to recreate the spreadsheet functions. It supports more than 280 spreadsheet functions."
• Calcapp. "If you can write a formula in Excel, you can build calculators, quote tools and field guides that your team and customers can use on any phone or in any browser." Its Starter plans are "$9 per month, Billed annually".
• Excel for the web. Microsoft offers "free access to Word, Excel, and PowerPoint using Microsoft 365 for the web". On a workbook embedded from OneDrive, Microsoft's help (dated December 18, 2025) says "Anyone who visits the webpage with this embedded file will be able to view it without signing in." Its co-authoring page (dated October 12, 2026) says that people working in the same workbook "can see each other's changes quickly—in a matter of seconds", so two people who use one shared copy as a calculator change each other's answers.

Which to pick. If the workbook must stay the single source and has Excel functions you can't rewrite, SpreadsheetWeb runs its Excel functions as they are, and Appizy's Cloud plans calculate on Appizy's server, so the formulas stay off the page. If people must sign in and write rows back to a table, Power Apps or AppSheet fit, at a price per user. If the calculation fits on a page (inputs in, a result and a few intermediate values out) and you want one link for the crew, the AI-written file is the quickest, and the rest of this guide is for it.

Get the formulas out of Excel

The AI writes what you give it. A list of every input, formula, and table, in calculation order, is also what you test the page against later.

1. See every formula at once. Microsoft's help: "Select Formulas and then select Show Formulas to switch between displaying formulas and results," or press Ctrl and the grave accent key (`). Look for constants typed into formulas, such as *1.05, and for cells that look like inputs but hold formulas.
2. Copy them as text. In an empty column beside each result, type =FORMULATEXT(B8). Microsoft says FORMULATEXT "Returns a formula as a string", the same text the formula bar shows. Copy that column, and paste it into your prompt as values.
3. Name the inputs. Under Formulas > Name Manager, Microsoft says you can "create, edit, delete, and find all the names used in the workbook". Names such as length_m and waste_pct make the AI's functions readable, and Formulas > Create from Selection names a block of cells from their labels.
4. Step through a long formula. Formulas > Evaluate Formula shows "the different parts of a nested formula evaluated in the order the formula is calculated." Write down those intermediate values for one case: they're what you compare when a test fails.
5. Export the lookup tables. Save each table, such as a price list or a material table, as CSV. Excel warns that "only the current worksheet will be saved", so save each sheet that holds a table on its own, and paste the CSV into the prompt.
6. Note what isn't a formula. Data validation lists become the page's drop-downs. Conditional formatting becomes a warning on the page. A macro is VBA, and the AI has to rewrite it as well: paste the module into the prompt, or leave that job in Excel.

A running example makes the rest concrete. Say your sheet orders concrete for a slab:

It assumes a rectangular slab of even thickness, and positive inputs. Those limits go into the prompt too.

The prompt to give ChatGPT, Claude, or Gemini

Paste this, with your own lists in place of the example's. If your AI takes the workbook as an attachment, attach it too, but keep the pasted list: it's the version you check against.

Rebuild my Excel calculator as one self-contained HTML file that people open on a phone.

Inputs (cell, name, unit, allowed range, default):
- B2 length, m, 0.5 to 100, 6
- B3 width, m, 0.5 to 100, 4
- B4 thickness, mm, 0 to 500, 100
- B5 waste allowance, %, 0 to 25, 5 (the cell holds 0.05 for 5%; the page takes 5)
- B6 truck capacity, m³, 1 to 12, 8

Formulas, in calculation order (from FORMULATEXT):
- B8 volume_m3 = B2*B3*B4/1000
- B9 order_m3 = CEILING.MATH(B8*(1+B5),0.5)
- B10 trucks = ROUNDUP(B9/B6,0)
- B11 last_load_m3 = B9-(B10-1)*B6

Lookup tables: [paste each CSV here, with its name]

Test rows (the inputs above in order, then B8 to B11, separated by tabs):
[paste the rows from Excel here]

Rules:
1. Write each formula as a plain JavaScript function with named inputs, in the same order of operations as the sheet, with the Excel formula in a comment above it. Don't fix or simplify anything the sheet does: list what you'd change instead.
2. Write the lookup tables into the file as JavaScript arrays. Don't load data from other websites, and don't use eval or new Function. Don't use a library that reads formula text.
3. Match Excel: ROUND rounds halves away from zero, and an empty box counts as 0 where an empty cell does.
4. My sheet shows 27.5 in B9 for 25 m³ with 10% waste, where JavaScript gets 27.500000000000004. So before CEILING or ROUNDUP, round the value to 15 significant digits.
5. Outside an input's allowed range, show a message under that box and no result.
6. Show each result with its unit and the sheet's decimals, and show the intermediate values (B8 to B11) under the result.
7. Use type="number" inputs with inputmode="decimal", a label with the unit above each box, and text at least 16px. It must work at 390px wide.
8. Put "Version 1.0" and today's date in the footer.
9. Add a test mode that opens when the address ends in #test, also when #test is added after the page has loaded. It runs the test rows above, written into the file, and has a box where I can paste more rows copied from Excel. In a pasted row, cells are separated by tabs (or by spaces if there are no tabs), an empty cell is an empty box, a number with % is that number (7.5% means 7.5), and commas inside numbers are ignored. For each row, run the page's own functions and show every output, the expected value, and PASS or FAIL. PASS means equal after rounding both to the decimals the page shows; for a value the page doesn't round, a difference under 0.000000001 times the expected value (under 0.000000001 when the value is below 1).
10. At the end, list every Excel function you couldn't match exactly.

The test mode in rule 9 is how you check the page: on your computer before you upload it, then on a phone. The checking guide covers it in detail. Rule 4 is there because of case 8 in the test table below: keep it only if your own Excel shows 27.5 for that row.

What the AI must not put in the file

On Convika, a page's own scripts run as written: inline scripts, buttons' onclick, any script from an https:// address (Chart.js, KaTeX, or MathJax from a CDN), Web Workers built from the page's own code, and WebAssembly. A few things stop, by the page's Content Security Policy:

• eval and new Function. The policy has no 'unsafe-eval'. MDN's page on script-src says that without it, "the following methods are blocked and won't have any effect", and lists eval(), Function(), and setTimeout given a string. A formula library that turns formula text into code this way stops too.
• Data from other sites. A script's fetch and XHR requests on a Convika page reach only the page's own address, plus, on Pro, the analytics tools Convika supports and the hosts you list for your own ad network. So the calculator can't read a live Google Sheet, an exchange-rate API, or a supplier's database: the numbers it needs go into the file.
• The workbook itself. A page that reads an .xlsx at run time still needs something to calculate it. SheetJS, which the AI answers suggest for reading workbooks in the browser, says that "If the actual results are needed in JS, SheetJS Pro offers a formula calculator component". Plain functions you can read and test are the better route.

In our test on November 6, 2026, we served a calculator page with the same Content-Security-Policy header Convika sends for a page on Free, and opened it in headless Chromium. eval("1+1") and new Function("return 1") both threw "EvalError: Evaluating a string as JavaScript violates the following Content Security Policy directive because 'unsafe-eval' is not an allowed source of script". A fetch to an exchange-rate API failed with "Refused to connect because it violates the document's Content Security Policy". Chart.js loaded from jsDelivr and drew, and the calculator's own functions ran.

Excel functions with no one-line JavaScript twin

These are the ones to name in the prompt, and to put a test case on.

Why each one differs, with Microsoft's examples and our test output, is in How to check that an AI-made calculator matches your Excel sheet.

Test it against the sheet

Run the same inputs through the sheet and the page, and compare every output, intermediate values included. Pick cases from your real jobs, then add the edges: a blank box, a zero, a value on a rounding step, the limits you put in the prompt, and every branch of every IF.

The slab sheet's test table, worked by hand in decimal arithmetic. On November 6, 2026 we ran all 8 rows, every column, through a calculator written to the prompt above, in its #test mode in headless Chromium: all 8 passed.

Fill the expected columns from your own Excel, not from a table like this one. Two rows here show why the test is worth running:

• Case 4 finds a quirk in the sheet. At 0 mm the sheet orders no trucks, and =B9-(B10-1)*B6 gives 0 - (-1 × 8) = 8 m³ for the last load. An AI that "fixes" it to 0 fails the test, and that's right: the page should match the sheet, and you fix the sheet and the page together, for example with =IF(B10=0,0,B9-(B10-1)*B6).
• Case 8 sits on a rounding step. In JavaScript, 25 × 1.1 is 27.500000000000004, so Math.ceil(x / 0.5) * 0.5 orders 28 m³, where decimal arithmetic gives 27.5. Rounding to 15 significant digits first, as rule 4 asks, gives 27.5. Run this row in your own Excel: if your sheet shows 28, take rule 4 out of the prompt and expect 28.

To paste rows into the test mode, select the cells from Length to Last load in your own table (not the Case column) and copy them. Copied cells can carry what a cell shows, such as a 7.5% shown as 8%. So first make every cell show all its decimals: keep a percent cell as a percentage and add decimal places until 7.5% shows as 7.5%, and set the other cells to General. The test mode reads 7.5% as 7.5. Paste the rows as Excel copies them, with tabs between the cells: an empty cell, like case 3's, keeps its place only between tabs.

The rows written into the file can be read by anyone who opens the page, so put made-up jobs there, and paste rows with a client's figures into the box instead.

Compare to a stated tolerance. For a result shown to 1 decimal, the page's value rounded to 1 decimal must equal the sheet's. For an intermediate value, a difference under 0.000000001 of its size (or under 0.000000001 for a value below 1) is the same number in both. Anything bigger is a different formula, a different rounding, or a different input. You stay responsible for checking the results against your own standard or code.

Publish the calculator for your team in 5 steps

1. Check the file opens as a page

Open the HTML file the AI gave you in your computer's browser and try the default inputs. Then add #test to the end of the address in the address bar and press Enter (reload the page if the test mode doesn't appear). The test rows written into the file run, and you can paste more from Excel. That's where the calculator first runs, before any upload. If you only see code, the file is saved with the wrong extension: HTML file shows code or a blank page has the fixes.

2. Upload it

Drop the file into the box below, or paste its code under Paste code, then click Get my preview link. Convika takes one .html or .htm file, up to 2 MB, and the box doesn't take an .xlsx. The preview link from the box works for 3 minutes with scripts and forms off, so the calculator shows its layout but doesn't calculate yet. Click Keep this page — free, no card and sign up: the page moves into your account, where its scripts run. With an account already, click Upload an HTML file on the dashboard, then Create my preview.

3. Choose who can open it

Click Publish page. Under Who can open this page?, choose:

• Public: "Anyone with the link can open it. It may show up in search results and in Convika's gallery." Click Next, and the first time, click Publish free. The page goes live with the Convika bar at the bottom.
• Private link (Pro): "Anyone with the link can open it, with no password or account. It stays out of search results and out of the gallery."
• Only people with the password (Pro): Convika's server checks the password before it sends the page.

A private link keeps the page out of search, but a forwarded link still opens it. For margins, prices, or a client's figures, choose the password. Either Pro choice opens an order for Pro ($12 a month, after a free 1-day trial with a card if your workspace hasn't had a subscription).

4. Run the test cases on a phone

Copy the address under Live URL and open it on your phone with #test at the end. The test rows written into the file run by themselves, so nothing has to be pasted on the phone; for other rows, email them to yourself and copy them from the email (a row with an empty cell needs its tabs, so check that it still lines up). Every row should pass before anyone else gets the link.

5. Send the link

Post the address in the crew's chat or email it. On the page's screen, Show QR code gives a code to print for the site office or the van. Each person can add the page to their home screen: the home screen guide has the steps for iPhone, iPad, and Android.

Who can open it, and what they can read

• The answer, and the formulas. Everyone who can open the page can also read its source, so the JavaScript formulas and any table in the file are readable to them. A password keeps out people who don't have it, not people who do. If the formulas themselves are the secret, a builder that calculates on its server, such as Appizy's Cloud plans, keeps them off the page.
• No sign-in by name. Convika doesn't limit a page to your company's email addresses, single sign-on, or named accounts. Everyone uses the same link, or the same password.
• Not an app install. The home screen icon opens the live page from its address. Don't count on it working without a connection.
• Counts, not names. The page's visitor stats show how many opened it and from where, never who: see how to see who visits your page.
• Results that come back to you. If the crew should send a result in, such as an order to the office, add a form to the page: Convika stores the entries and emails them to you, and Free shows 50 entries a month. How to make the form on your AI-made page work has the steps.

New versions at the same link

When the sheet changes, change the page the same way: update the formula list and the test rows, ask the AI for the whole corrected file, and run its #test on your computer. Then, on the page's screen, under Update from an HTML file, click Upload a new version and Upload as a new version. You get a private preview: click Open preview, then Open in a new tab, add #test to the end of the address, and reload the page. The preview link works for 3 minutes; if it has ended by the time you reload, click Open preview and Open in a new tab again. When every row passes, click Publish v2 at the same link (with your version number). The address stays the same, so every phone, home screen icon, and printed QR code opens the new version.

Keep one address per tool, and put the version number in the page's footer, so anyone can tell you which version gave an answer. If you upload the file as a new page instead, it gets a second address, and the old one stays live with the old formulas: see how to update an AI-made page without changing its URL. Free keeps the last 10 versions of a page and Pro the last 50, so you can roll back.

A second calculator. A new Free workspace publishes 1 page at a time. Publish a second, different page as Public and Convika asks you to choose: Light ($3 a month on top of Free, for up to 5 live pages; the Convika bar stays), or Swap it in for the live page (free), which turns the live page back into a draft whose link stops opening. Pro publishes up to 100 pages, with private links, passwords, and 3 members to share the work.

Calculators built this way

Each of these guides takes one kind of sheet through the route above, with the prompt to give your AI and a test table to check the page against your Excel:

• Excel macros on iPad: a VBA macro that Excel for iPad won't run, rewritten as a web page.
• A quote calculator from a price sheet: a staff page with costs and margins behind a password, and a client page with prices and a quote request form.
• Pump head and pipe friction loss: total dynamic head with Darcy-Weisbach or Hazen-Williams friction, and fitting losses.
• NPSH available: open, pressurized, and boiling tanks, with altitude and vapor pressure tables.
• Voltage drop: the voltage drop formulas with K and NEC Table 8 values.
• Duct size: equal friction sizing for round and rectangular ducts, with a solver in place of Goal Seek.
• Manning's equation: open channel flow in rectangular, trapezoidal, and partly full pipe sections, with normal depth solved in place of Goal Seek.
• Slurry pipeline: mixture density, deposition velocity, and head loss.

Frequently asked questions

Can ChatGPT turn my Excel spreadsheet calculator into a web app that works on a phone?

Yes, if you give it the inputs, the formulas, and the units, and ask for one HTML file with the formulas as JavaScript functions. ChatGPT, Claude, and Gemini can all write that file. The AI's word that it matches isn't a test: run your own cases through the sheet and the page, then publish the file at a link.

How do I convert an Excel calculation sheet into a simple HTML calculator my team can open in a browser?

List every input and formula with FORMULATEXT, paste the list into ChatGPT, Claude, or Gemini, and ask for a single HTML file with plain JavaScript functions and no eval. Test it against the sheet with 6 to 20 cases. Then publish the file on a host and send the link.

Can I convert an Excel spreadsheet to a web application for free?

Yes. An AI can write the HTML file for free, and Convika publishes it as a Public page on the Free plan, with the Convika bar. SpreadsheetWeb also has a free tier, with 1 application, 300 sessions a month, and its branding. Keeping the page out of search, or behind a password, needs Pro on Convika.

What's the easiest way to turn a spreadsheet with formulas into a mobile calculator without coding?

A builder that reads the sheet: SpreadsheetWeb runs the workbook's Excel functions as they are, and Appizy and SpreadsheetConverter convert it, with no code from you. The AI route needs no code from you either, but it needs a test: the AI rewrites the formulas, and only your test cases show that it got them right.

Will the AI-made calculator keep my formulas private?

Not from the people who can open it. A web page's formulas are in its source, which anyone with the page can read. A password on Convika keeps out everyone without it. To keep formulas hidden from users too, use a tool that calculates on its server: Appizy's Cloud plans say "end users only see the interface and the results".

Can the calculator pull prices or data from a Google Sheet or an API?

Not on a Convika page. A script's fetch and XHR requests on a Convika page reach only the page's own address, plus, on Pro, the analytics tools Convika supports and the hosts you list for your own ad network. Put the tables in the file, and publish a new version when they change.

Can I use SheetJS to run my workbook in the browser?

SheetJS reads workbooks in the browser, but its docs say that for calculated results, "SheetJS Pro offers a formula calculator component". For a calculator, ask the AI for plain functions instead. You can read them, test them, and they need no library.

Does the web app work offline, like an installed app?

Don't count on it. A Convika page loads from its address each time it's opened, and Convika doesn't make it an installed app. If the crew works without signal, AppSheet and Calcapp's Business plan list running apps offline, or the sheet itself stays on the device.

How do I update the calculator without sending everyone a new link?

Upload the new file on the page's screen under Update from an HTML file. Click Open preview, then Open in a new tab, add #test to the end of the address, and reload the page to run your test rows (within 3 minutes, before the preview link ends). Then click Publish v2 at the same link (with your version number). The address doesn't change, so links, home screen icons, and QR codes open the new version.

Sources

• Display or hide formulas (Microsoft Support) (dated April 24, 2026; read November 6, 2026)
• FORMULATEXT function (Microsoft Support) (dated January 1, 2026; read November 6, 2026)
• Define and use names in formulas (Microsoft Support) (dated April 28, 2026; read November 6, 2026)
• Evaluate a nested formula one step at a time (Microsoft Support) (dated May 5, 2026; read November 6, 2026)
• Import or export text (.txt or .csv) files (Microsoft Support) (dated May 11, 2026; read November 6, 2026)
• ROUND function (Microsoft Support) (dated January 1, 2026; read November 6, 2026)
• ROUNDUP function (Microsoft Support) (dated January 1, 2026; read November 6, 2026)
• CEILING.MATH function (Microsoft Support) (dated February 3, 2026; read November 6, 2026)
• VLOOKUP function (Microsoft Support) (dated January 1, 2026; read November 6, 2026)
• IRR function (Microsoft Support) (dated January 29, 2026; read November 6, 2026)
• Use Goal Seek to find the result you want by adjusting an input value (Microsoft Support) (dated October 6, 2025; read November 6, 2026)
• Remove or allow a circular reference in Excel (Microsoft Support) (dated July 7, 2026; read November 6, 2026)
• Excel incorrectly assumes that the year 1900 is a leap year (Microsoft Learn) (dated March 30, 2026; read November 6, 2026)
• Math.round() (MDN) (last modified July 10, 2025; read November 6, 2026)
• CSP: script-src (MDN) (last modified August 12, 2026; read November 6, 2026)
• Formulae (SheetJS docs) (no date on the page; read November 6, 2026)
• Glide pricing and Glide's Excel page (no date on the pages; read November 6, 2026)
• AppSheet pricing and Define app formulas and initial values (AppSheet Help) (no date on the pages; read November 6, 2026)
• Power Apps licensing and pricing (Microsoft) (no date on the page; read November 6, 2026)
• Create a canvas app based on Excel data (Microsoft Learn) (dated May 19, 2026; read November 6, 2026)
• Share a canvas app in Power Apps (Microsoft Learn) (dated September 17, 2026; read November 6, 2026)
• SpreadsheetWeb Hub pricing (modified July 28, 2026; read November 6, 2026)
• SpreadsheetConverter price list and its JavaScript calculator page (no date on the pages; read November 6, 2026)
• Appizy pricing (no date on the page) and Appizy functions and formulas (reviewed May 4, 2025; both read November 6, 2026)
• Calcapp and Calcapp pricing (no date on the pages; read November 6, 2026)
• Free Microsoft 365 Online (Microsoft) (no date on the page; read November 6, 2026)
• How to add an embedded document or picture into a webpage (Microsoft Support) (dated December 18, 2025; read November 6, 2026)
• Collaborate on Excel workbooks at the same time with co-authoring (Microsoft Support) (dated October 12, 2026; read November 6, 2026)