Who builds this, and how

Who runs this

That is the whole of it. This is a small operation, not a media company, and there is no newsroom behind the calculators. We are not going to pad this page with an invented team, an invented founding date or an invented user count, because the point of the page is that you should be able to check what we say — and a claim you cannot check is worth nothing on a page about money and health.

The CNPJ is a public Brazilian company register number. Publishing it exposes nothing that is not already searchable, and it means that a legally identifiable entity stands behind every number on this network. The same identification appears on the privacy policy and the contact page, because data protection law wants to know who is responsible, not just how to send a message.

Why this network exists

Free calculators are everywhere and most of them are bad in one of two specific ways.

The first is that the arithmetic is wrong. Not wrong in an exotic edge case — wrong in the ordinary case, because someone typed a formula from memory into an inline script and nobody ever checked it. A fee calculator applies the rate to the item price and forgets the shipping the fee is also charged on. A break-even calculator multiplies cost by one plus the commission instead of dividing by one minus it. Nobody notices, because the output looks exactly like a calculated answer.

The second is worse and much more common: the tool hides its own limits. It prints one number to two decimal places when the underlying model has a spread of forty per cent. It puts a green badge next to a result that no model can justify. It answers a question that needs a professional, and then buries the disclaimer in grey six-point type at the bottom of the page, below the ads, collapsed behind a chevron.

A number carries authority just by being a number. Producing one and staying quiet about what it cannot tell you is the failure we built this network to avoid.

How a tool is actually built

The rule is simple and it is enforced by the file layout: the mathematics lives in its own module, outside the page. Twenty-seven of the live tools have one — a plain JavaScript file of pure functions, no DOM, numbers in and numbers out, sitting next to the interface that consumes it.

That is not tidiness for its own sake. When the arithmetic is buried in an inline script, the only way to check it is to open the page and squint at the result — which is exactly how a wrong calculator stays wrong for years. When it is a module, a script can call it directly and compare against a value that came from somewhere else.

That script is scripts/verify-math.mjs. It currently runs 92 checks and they all pass. The important part is not the count, it is the rule the file follows: an expected value that was derived by re-running the same formula proves nothing. So every case in it has an answer that came from outside the code — an internationally agreed definition, an algebraic identity, or a calculation done by hand.

Concretely, that means checking that an inch is exactly 0.0254 metres and a pound is exactly 0.45359237 kilograms rather than the rounded values that circulate; that one year at a 4.5% APY yields exactly 4.5% at every compounding frequency, because that is the definition of APY; that black on white gives a contrast ratio of exactly 21:1, the WCAG maximum; that the spreadsheet date epoch is 1899-12-30 and not 1900-01-01; and that the two branches of the CKD-EPI 2021 equation meet where they are supposed to meet. One of the kidney-function reference values in that file was originally wrong because it was written from memory, which is precisely the failure the file exists to catch.

Content has a gate of its own. A build script fails the release of any page it audits that comes in under 1,200 words, five sections or four answered questions, so an explanation cannot quietly decay into a heading and a form. Forty-four of the tools are inside that gate. The rest are marked exempt in the site register, one by one and in writing, because for those the long explanation would be work that never turns into a reader.

The tools tell you when not to use them

This is the part we would most like to be judged on, because it is the part that costs something. Every one of these is a decision in the source code, not a line of marketing.

The blood alcohol calculator never returns a single number. Every output is a range, in the result card, in the chart — which is a band with no centre line — and in the time-to-zero. Individual variation in body composition, food, enzyme genetics and drinking pace is wider than the gap between "under" and "over" any legal limit, so a single figure would be invented precision. There is no green state and no traffic light anywhere in it, because green communicates permission and there is no permission to give. The phrases "safe to drive", "under the limit" and "you can drive" do not appear in either language, and the lowest result is the one written most carefully, because that is exactly where a bad calculator slips into telling you that you are fine.

The wire size calculator refuses to answer. Cable sizing is two independent problems — current-carrying capacity, which protects the cable, and voltage drop, which protects the equipment — and the answer is the larger of the two. If no size in the table satisfies one of them, the tool returns a failure and no size at all. Returning the winner of the criterion that did have a solution would mean printing a gauge that melts under the load, with the full appearance of a calculated answer.

The water intake calculator has a ceiling, because drinking too much water kills people through dilutional hyponatraemia. A healthy kidney clears somewhere around 0.8 to 1.0 litres of free water per hour, and the tool says so when a recommendation approaches it.

The severance calculator states in the result itself that the binding figure is the one on the signed settlement document, not the one on our page, and lists what can move it.

What we do not do

• We do not sell your data. There is nothing to sell: for ordinary browsing we store a salted hash rather than an IP address, which is why the privacy policy admits we usually cannot find records tied to you even when you ask.
• We do not ask you to sign up. Sixty-two of the sixty-three tools have no account, no login and no email field. The single exception is CS2 skin price alerts, which cannot email you an alert without knowing where to send it, and which says so.
• We do not process your files on a server. In the SVG to PNG converter, the PDF tools and the image beautifier, the file is read and written in your browser. There is no upload endpoint to call, which you can confirm in your browser's network tab. The consequence we accept is that if you close the tab, the work is gone, and we have no copy to send you.
• We do not gate anything behind a paywall or a watermark. Advertising pays for the network, which the cookie policy covers in full.

Where we were wrong

Every one of these shipped or nearly shipped, and every one is documented in the source where it was fixed. We publish them because a page claiming to be careful is worth nothing without examples of the carelessness it caught.

There is also a whole category of error that never reaches a user and is worth naming: the off-by-one. Dividing a length by a spacing gives you the number of gaps, not the number of posts, joists or studs — and the missing one is always the one at the edge, which is where the load has no support. Several tools in the construction group carry an explicit comment at that line for exactly that reason.

How to correct us

Write to [email protected]. A report that a calculator is wrong is the most useful message we receive, and corrections to the arithmetic are the only work here that jumps the queue — an incorrect calculator is worse than no calculator.

To be actionable, a report needs the tool, the exact values you entered, the result you got, the result you expected, and ideally the source that says otherwise: a formula, a code section, a published table. "It is wrong" cannot be acted on. "At 40 A over 60 m in copper it returns 6 mm² and NBR 5410 gives 10 mm²" gets fixed.

If we got something wrong here, we would rather find out from you than not find out. The terms of use set out which tools need which kind of professional, tool by tool, and the contact page covers privacy requests, security disclosure and everything else.