About / zerouploads
Tools that show their work
zerouploads is a small, growing set of free calculators and converters. One job to a page, and every page shows its working: the answer written out in words, the formula it came from, and examples worked through with real numbers.
01 / The idea
A number on its own is not an answer
Most online calculators hand you a figure and stop there. You cannot see whether it rounded, which definition of a month it used, or whether the fourth decimal place means anything. When the figure matters — a repayment, a dose, a length of timber — that is not much use.
So each page here states its answer as a sentence, gives the formula, and works through examples. If your figure and ours disagree, the page should tell you where the difference comes from rather than leaving you to guess. That is the whole proposition, and it is the reason there are 41 tools here and not five hundred.
1 cm 0.3937 in
02 / The rules
Where the figures come from
- Exact constants, not rounded
- An inch is exactly 2.54 centimetres — a definition agreed between the English-speaking standards bodies in 1959, not a measurement. Where a conversion has an exact factor we use it, and convert through one base unit, so nothing picks up rounding error on the way through.
- Rounded once, at the end
- Interest and repayments run at full precision and are rounded where they are displayed, never at each step. Rounding early is how a repayment schedule ends up a few pounds out by year twenty.
- Dates by the registrar's rule
- Age counts whole years and months first, then the days left over, and clamps to the end of a short month — so someone born on 31 January is one month old on 28 February. Tools that convert to days and divide by 30.44 give a slightly different answer; neither is wrong, they answer different questions. Ours says which one it answered.
- Checked on every build
- The arithmetic lives in plain functions with tests beside them — known values, the awkward boundaries, and the round trip back. A converter that is wrong in the fourth decimal place is worse than no converter, so the build fails rather than ship one.
03 / How it runs
In your browser, on your device
The calculators are arithmetic. They run in the page as you type, with nothing sent anywhere, which is why the answer is there before you have finished typing the second number.
When tools that handle files arrive — images, documents — they will work the same way: the file is read and processed by your browser and never uploaded. That is a structural choice rather than a promise to trust. There is no upload endpoint here to send a file to, and adding one would mean rebuilding how the site works.
No account, no sign-up wall, no paid tier that unlocks the result. Every page is a plain document that works with JavaScript off, which is also the reason the answers are written out in text rather than only computed into a box.
04 / Today
41 tools, 5 collections
That is a deliberately small number. A page that cannot explain its own answer is not worth publishing, and writing that explanation is slower than wiring up the widget. More are being written; each one arrives when its page can stand on its own.
zerouploads is made and maintained by one person, Tushar. If a figure here ever disagrees with your own working, that is the one bug on this site worth taking seriously.
See the tools