What is a Unit Converter?
A unit converter turns a measurement in one system into the equivalent in another. The conversion itself is a single multiplication by a ratio — one inch is exactly 0.0254 metres, one pound is exactly 0.45359237 kilograms — which is why most of the answers here are exact rather than rounded.
The one exception is temperature, which is affine rather than proportional: 0 °C is 32 °F, not 0 °F, so a scale factor alone cannot describe it. Fahrenheit and Celsius are converted by first going to Celsius and then out again, and Kelvin is Celsius shifted by 273.15. Everything else in the tool follows the international yard and pound agreement of 1959 for imperial units and the SI definitions for metric ones.
Because the conversion factors are fixed, the useful part of a unit converter is the table underneath the answer: entering one value shows it in every unit in that category, so you can read the figure you need without converting twice.
How to convert between units
- Pick a category across the top: Length, Weight & mass, Area, Volume, Temperature, Speed, Data size, Time, Pressure, Energy or Angle. The two dropdowns change to that category's units.
- Type the value you want to convert. Thousands separators are accepted and commas are ignored, so both 1500 and 1,500 parse as the same number.
- Choose the From and To units. Use Swap to reverse the direction without re-selecting anything.
- Read the result, then look at the table below it. The table shows the same starting value in every unit in the category, with the unit you selected highlighted — which is often faster than converting twice.
Unit Converter limits and rules
| Item | Limit |
|---|---|
| Length | Nanometre to nautical mile, including inch, foot, yard and statute mile |
| Weight & mass | Milligram to tonne, plus ounce, pound and stone |
| Area | Square centimetre to square mile, including hectare and acre |
| Volume | Millilitre to gallon, with US and UK fluid ounces and gallons as separate units |
| Temperature | Celsius, Fahrenheit and Kelvin — handled as an affine conversion, not a factor |
| Speed | Metre per second, km/h, mph, feet per second and the nautical knot |
| Data size | Decimal (kB, MB, GB, TB) and binary (KiB, MiB, GiB, TiB) units as separate entries |
| Time | Nanosecond to year, where a month averages 30.4375 days and a year is 365.25 days |
| Pressure | Pascal, hectopascal, kilopascal, bar, psi, atmosphere and millimetre of mercury |
| Energy | Joule, kilojoule, calorie, kilocalorie, watt hour, kilowatt hour and BTU |
| Angle | Degree, radian, gradian and turn |
| Precision | Shown to 10 significant figures; values below 1e-6 or above 1e15 switch to exponent notation |
| Not covered | Currency (rates change daily), fuel economy (it is inverse, not proportional) and date arithmetic |
When to use it
- Following a recipe written in cups and tablespoons while working in millilitres, including the US-versus-UK fluid ounce difference that causes the most common baking mistakes.
- Reading a specification from a datasheet in inches, pounds or psi and restating it in metric for someone who works in millimetres, kilograms and bar.
- Checking a body weight or height between stones and pounds, or feet and inches, and the metric figures a form asks for. The BMI calculator takes either.
- Sizing a file transfer — megabytes against mebibytes is the discrepancy behind every "why is my 1 TB drive only 931 GB" question.
- Converting speed for a foreign road trip, where the difference between 90 km/h and 56 mph matters.
Is it private?
Everything runs inside your browser. Your text and files are never uploaded, never stored and never seen by anyone else — including me. You can use the tool with the network tab open and watch no request leave the page. Closing the tab erases the input.
Frequently asked questions
Because two systems share the name. A US fluid ounce is 29.5735 mL and a UK fluid ounce is 28.4131 mL; the gallons diverge further still. Both are listed separately so you can pick the one your recipe or datasheet means.
Both, depending on who is counting. Storage makers use decimal SI prefixes — 1 MB is 1,000,000 bytes. Operating systems report binary multiples, which are correctly called mebibytes — 1 MiB is 1,048,576 bytes. The tool lists them as separate units so the distinction stays visible.
The factors are the officially defined values, so the arithmetic is as exact as floating-point arithmetic allows. Displayed to 10 significant figures, that is far beyond any practical measurement — the limit on accuracy is the input, not the conversion.
Yes. Entering -40 gives the same reading in Celsius and Fahrenheit, which is the only point where the two scales meet. Kelvin values below 0 are physically meaningless but the tool will still convert them.
No. Exchange rates change continuously and would need a live feed, so any offline figure would be wrong by the time you read it. This tool converts only units whose factors are fixed by definition.
Related tools
Written and maintained by Md. Nur Hossain Repon.