Free Online Converter & Calculator Tools

Why these tools run in your browser

Most online converters send whatever you type to a server, process it there, and send the result back. That is invisible to you and usually harmless, but it means your input has left your machine. For a length conversion nobody cares. For a JWT containing a session token, a configuration file with credentials, or an API response with customer data, it matters considerably.

Every tool here is implemented in JavaScript that runs inside your browser. Once the page has loaded, the conversion itself involves no network request at all. You can verify this: open your browser's developer tools, switch to the Network tab, and use any tool on this site. Nothing is sent.

Two practical consequences. Tools work offline once the page is loaded, and they are safe to use with data you would not paste into an unknown server.

What is here

Unit converters

Fourteen converters covering the physical quantities that come up in everyday life and technical work: converting a recipe from cups to milliliters, a US height in feet and inches to centimetres, tire pressure from bar to PSI, or engine output between kilowatts, horsepower, and PS.

Each page includes the conversion factors used, why they are what they are, and the traps specific to that quantity. Area conversion, for instance, requires squaring the length factor, which is why one square meter is 10,000 square centimetres rather than 100. Volume has the US and UK gallon problem. Data size has the decimal versus binary confusion that makes a 1 TB drive show as 931 GB.

Developer tools

Eighteen tools for the small tasks that interrupt development work: decoding a Base64 string, inspecting a JWT payload, formatting a JSON response, working out what a cron expression does, calculating a subnet range, or converting a .NET tick value to a date.

These benefit most from running locally, since the input is frequently a real token, a production configuration, or a live API response.

How the pages are built

Each tool page follows the same structure: the working tool at the top, then an explanation of how the conversion or operation actually works, worked examples, a reference table, practical use cases, and answers to the questions that come up most often.

The explanations are there because knowing why a conversion works usually prevents the next mistake. Understanding that temperature conversion needs an offset explains why a 10-degree temperature difference converts differently from a 10-degree temperature. Understanding that Base64 is an encoding rather than encryption prevents using it to "protect" a password.

Frequently asked questions

Is any of this free?

Yes, all 32 tools, with no account, no usage limit, and no paywalled features. The site is funded by advertising.

Is my input really not uploaded?

Correct. All processing happens in your browser. You can confirm it in the Network tab of your browser's developer tools, no request is made when you use a tool. Note that the advertising shown on the page does communicate with Google, which is described in the privacy policy, but that is entirely separate from the tools themselves.

Do the tools work offline?

Once a page has finished loading, yes. The conversion logic is already in your browser at that point.

Do I need to create an account?

No. There is no registration, no login, and no stored user data.

Can I use these tools for professional work?

The conversion factors are the internationally defined values and the pages state which are exact and which are approximations. That said, the terms of use apply: verify results independently before basing safety-relevant, financial, or legal decisions on them.

Which browsers are supported?

Any current browser. One feature is limited: the screen colour picker in the colour converter uses an API currently available only in Chrome, Edge, and Opera. Everything else works everywhere.