Sample Size — Proportion Surveys
Approximate sample size for estimating a proportion at a given margin and confidence.
How it works
- 1Enter your values in the fields above
- 2Click "Sample size" — all math runs in your browser
- 3View your results instantly
What to do next
About Sample Size Calculator
Sample Size Calculator is a self-contained calculation workspace. Approximate sample size for estimating a proportion at a given margin and confidence. Open the page, get the result, close the tab — that is the entire workflow.
Sample Size Calculator fits naturally into the workflow of engineers sanity-checking conversions and parents helping with maths, both of whom typically need a fast result inside the browser. There is no learning curve to budget for: anyone who has used a typical web upload form can complete a run on the first try.
Reach for Sample Size Calculator when you need a predictable result on a single file. The page works on the first visit, the controls are visible without a menu, and the output is delivered the moment the engine finishes.
Under the hood, Sample Size Calculator uses standard browser APIs to do the actual work. Input runs through the same engine, with a per-file ceiling of 0 MB so memory usage stays predictable on lower-end laptops and tablets. The engine ships as part of the page bundle, so once the page is loaded the tool keeps working even if your network connection drops.
The browser sandbox isolates the page's JavaScript from the rest of the system, the same way it isolates every other tab you have open. Sample Size Calculator works inside that sandbox: it reads the file you give it, processes it with standard browser APIs, and writes the result back. Nothing leaves the page's memory unless you choose to download or copy it.
Once you have used Sample Size Calculator, the natural next steps depend on what you are doing with the result. Common follow-ups include Confidence Interval Calculator, Probability Calculator, and Binomial Distribution PMF. These are surfaced on the page so you do not have to hunt the catalog manually.
The 0 MB ceiling on input size is the only fixed limit. Output files are produced in standard formats that every common viewer recognises, and the tool runs the same way regardless of how many times you have used it during the session.
Sample Size Calculator is honest about scope: it handles a single, well-defined calculation step. Specialist edge-case work — uncommon formats, very large inputs, or pipelines that need scripting — is what dedicated desktop apps are for. This page handles the common case quickly.
Output handling is intentionally boring: Sample Size Calculator produces a single output file and triggers your browser's standard "save" behaviour. If you have a default download folder configured, that is where it will land. There is no Favtoo-side history of jobs you have run.
Sample Size Calculator is structured around the idea that a useful tool should be its own page. Open the page, do the work, close the tab — the page is the entire product. There is no onboarding flow because there is nothing to onboard into.
Sample Size Calculator fits the gap where opening a desktop app feels heavy and writing a script feels overkill. The page handles the common calculation task with sensible defaults so a single visit usually completes the job; for highly specialised work, a dedicated desktop application can offer more knobs to turn.
Tips from users who reach for Sample Size Calculator regularly: process one input first to confirm the settings produce what you expect before committing to a batch; treat the page as the working surface and avoid leaving large jobs running in a backgrounded tab where the browser may throttle JavaScript; and if a particular file fails, check whether the source is intact by opening it in its native viewer — most "tool errors" are actually input errors.
For most failure modes, refreshing the page and re-running the job is enough — the engine has no persistent state to corrupt. If the same input fails twice in a row, the input itself is most likely the problem (a truncated file, an unexpected variant of the format, or a stream the engine does not recognise).
That is essentially everything Sample Size Calculator does and how it does it. Open the tool above, drop in your input, and the work happens in the page. If you find yourself reaching for it often, bookmark the page — it loads quickly on subsequent visits, and your most-recent settings are remembered for the rest of the session.
How it works
- 1Open Sample Size Calculator in your browser. The page loads quickly and the tool is ready to use the moment it becomes interactive.
- 2Drop a calculator file onto the upload area, or click to pick one from your device.
- 3Pick any non-default settings you need. Most users leave the defaults alone for the first run and only revisit if the result needs tuning.
- 4Hit the run button. standard browser APIs does the work in your browser tab.
- 5Download the result. The file is generated in your browser and saved through your normal download flow.
- 6Repeat the process for additional inputs whenever you need to. The page stays loaded, so subsequent runs are quick.
Common use cases
- Compare two scenarios side by side without spinning up a spreadsheet using Sample Size Calculator.
- Forecast a fitness target without a paid app.
- Estimate a finance schedule before approaching a bank.
- Convert a measurement on the fly while shopping.
- Split a restaurant bill cleanly between a group.
- Confirm a unit conversion before quoting it in a report.
- Convert a foreign currency amount into your local one.
- Plan a project budget on a phone in a meeting.
- Sanity-check a quote before sending it to a customer.
FAQ
How do I use the Sample Size Calculator?
Enter the fields shown, then click the calculate button. Results appear instantly in your browser without uploading data.
Does this tool send my numbers to a server?
No. Calculations run locally in your browser using JavaScript on your device.
What if I get an error message?
Check that all required inputs are valid numbers (no empty fields where a value is needed) and that constraints like positivity are satisfied.
Can I use decimals?
Yes — decimal numbers are supported wherever a numeric field is shown, subject to normal floating-point limits.
Is an account required?
No account or sign-up is required to use this calculator.
How accurate are the results?
Results follow standard floating-point arithmetic in JavaScript; for critical applications verify independently.
Does Sample Size Calculator support batch processing?
Sample Size Calculator processes one input at a time by design — it keeps memory usage predictable on lower-end devices and makes results easier to verify. To handle a folder, run the tool once per file; the page stays loaded between runs and remembers your last-used settings, so the second run is essentially instant.
Which file formats does Sample Size Calculator accept?
The accepted formats are listed in the upload area on the tool itself. If your input is in a format that is not directly supported, convert it first using one of Favtoo's converter tools — every Favtoo converter outputs a file that is a clean input to the next tool in the chain.
Does Sample Size Calculator match what professional tools produce?
Sample Size Calculator is built on standard browser APIs, which is the same class of engine used by professional calculation pipelines. For deterministic operations, the output is byte-identical to what an equivalent CLI run would produce; for operations involving a codec or a model, the result is well within the range of what comparable tools generate. If you have a specific reference output you need to match, run a small test job first to confirm the configuration produces what you expect.
How long does Sample Size Calculator take to process a file?
Most jobs finish in seconds. Speed scales with input size and with how many CPU cycles your browser tab has available — the engine runs in your browser, so it shares resources with whatever else you have open. For inputs near the 0 MB ceiling, expect anywhere from a few seconds to roughly a minute on a typical laptop. Closing other heavy tabs noticeably speeds things up.
How many times per day can I use Sample Size Calculator?
Inputs are capped at 0 MB per file, which keeps memory usage stable across phones, tablets and older laptops. You can run Sample Size Calculator as often as you need; every run produces a full-quality result.
Is Sample Size Calculator licensed for business use?
Sample Size Calculator can be used for personal and commercial work alike — there is no separate "business" licence to purchase. The output you generate is yours to use however you want, including in client deliverables, internal documents, or commercial products. Favtoo's only ask is fair, individual use; the tool is not designed to be embedded as a backend service or wrapped behind an API for resale.
Is there a desktop version of Sample Size Calculator?
No installation is needed. Sample Size Calculator runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use Sample Size Calculator on any computer you have temporary access to without leaving anything installed on it.
Is it safe to use Sample Size Calculator on confidential files?
Your file is processed inside your browser by standard browser APIs. The engine reads the file's bytes from your tab's memory, computes the result, and writes the result back into the tab. You can confirm what the page does by opening developer tools and watching the Network tab during a run — the requests you see are for the tool's static assets only.
What does Sample Size Calculator do that command-line tools do not?
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. Sample Size Calculator sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common calculation operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.