Summary: convert units free and private
A unit converter changes a measurement from one unit to another, such as miles to kilometres or Fahrenheit to Celsius. To convert units for free and privately, pick one of the 10 categories above, type a value, and choose the From and To units. The result and a list of every other unit in that category update as you type. The conversion runs in your browser; nothing is uploaded, and you can check the Network tab in DevTools to see that.
The formula is result = value × (size of the From unit ÷ size of the To unit), with every size stored in one base unit per category. For example, 5 mi = 5 × (1,609.344 ÷ 1,000) = 8.04672 km. Temperature is the exception because its scales start at different zeros: °F = °C × 9/5 + 32 and K = °C + 273.15.
For one kind of measurement, the Length Converter, Weight Converter and Temperature Converter have dedicated pages.
Table of Use: categories, units and worked examples
| Category | Units included | Example result |
|---|---|---|
| Length | km, m, cm, mm, mi, yd, ft, in, nmi | 5 mi = 8.04672 km |
| Weight | kg, g, mg, tonne, lb, oz, stone, US ton, UK ton | 150 lb = 68.0388555 kg |
| Volume | L, mL, m³, ft³, in³, US gal/qt/pt/cup/fl oz/tbsp/tsp, UK gal/pt/fl oz | 1 US cup = 236.5882365 mL |
| Temperature | °C, °F, K | 100 °F = 37.77777778 °C |
| Area | m², km², cm², ha, acre, mi², yd², ft², in² | 1 acre = 43,560 ft² |
| Speed | m/s, km/h, mph, knots, ft/s | 100 km/h = 62.13711922 mph |
| Data storage | bit, B, kB, MB, GB, TB, KiB, MiB, GiB, TiB | 500 GB = 465.6612873 GiB |
| Time | ms, s, min, h, d, wk, average month, average year | 1 year = 365.2425 days |
| Pressure | Pa, kPa, MPa, bar, psi, atm, mmHg | 1 atm = 14.69594878 psi |
| Energy | J, kJ, cal, kcal, Wh, kWh, BTU | 2,000 kcal = 8,368 kJ |
Features
- All Conversions list. One value shown in every other unit of the category at once, so you can find the unit you need.
- Exact definitions. Factors such as 1 in = 2.54 cm and 1 lb = 0.45359237 kg are the legal ones; time uses Gregorian averages for a month and a year.
- Decimal and binary data units. kB, MB, GB and TB (powers of 1,000) sit next to KiB, MiB, GiB and TiB (powers of 1,024).
- US and UK volumes. Gallons, pints and fluid ounces in both systems, plus cups, tablespoons and teaspoons in US sizes. For measuring a container first, see the Volume Calculator.
- Swap, copy and pin. One button reverses the units, a copy icon saves the result as text such as "5 mi = 8.04672 km", and pins keep your favourite units at the top.
- Flexible input. 1.5 and 1,5 both work, and so does scientific notation such as 6.02e23.
- Plain warnings. A note appears for temperatures below absolute zero, and for numbers beyond what a computer can hold (about 1.8e308).
How to Use the Unit Converter
- Choose a category with the buttons at the top, from Length to Energy.
- Type the Value. The field starts at 1.
- Pick the From and To units from the two dropdowns. The arrows button between them swaps the two.
- Read the result in the highlighted box and use the copy icon if you need it elsewhere.
- Scan All Conversions for the same value in every other unit, and pin the ones you use most.
Who Can Use It
- Cooks turning cups, tablespoons and fluid ounces into millilitres.
- Travellers reading road signs and forecasts in miles, mph and °F. The Speed Calculator and Fuel Cost Calculator cover the next step.
- Home and garden planners comparing acres, hectares and square feet; the Area Calculator finds the area from dimensions.
- IT and media users checking why a drive or file size looks different on two devices.
- Students and engineers working with pressure, energy and scientific notation, alongside the Scientific Calculator or Percentage Calculator.
- Shoppers and expats pricing goods abroad, with the Currency Converter for money and the Time Zone Converter for clocks.
Frequently Asked Questions
How do I convert metric units to imperial units?
Choose the category, set the metric unit under From and the imperial or US unit under To, then type the value. The converter multiplies by exact factors such as 1 inch = 2.54 cm, 1 pound = 0.45359237 kg and 1 mile = 1,609.344 m, so 10 km comes out as 6.213711922 mi. The swap button reverses the direction.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9: °C = (°F − 32) × 5/9. So 100 °F is about 37.78 °C, and −40 is the same on both scales. In the converter, open Temperature, choose Fahrenheit under From and Celsius under To. Kelvin is also there (K = °C + 273.15), with a warning for values below absolute zero.
What is the difference between MB and MiB?
A megabyte (MB) is 1,000,000 bytes, the decimal unit drive makers use; network speeds are quoted in decimal megabits per second (Mbps), and 1 MB = 8 Mb. A mebibyte (MiB) is 1,048,576 bytes (1024 × 1024), which some operating systems label as MB. That is why a 500 GB drive shows as about 465.66 GiB. The Data Storage category lists both families: kB to TB and KiB to TiB.
Why do US and UK gallons and cups differ?
They come from different historical definitions. A US gallon is 3.785411784 litres and a UK (imperial) gallon is 4.54609 litres, about 20% larger. A US fluid ounce is 29.57 mL and a UK one is 28.41 mL. The cup here is the US cup, 236.59 mL, so a recipe written for a 250 mL metric cup will differ slightly.
How accurate is the unit converter?
Where a legal definition exists the factor is exact, for example 1 inch = 2.54 cm or 1 atmosphere = 101,325 Pa. Results show about ten significant digits, and numbers of 1e15 or more, or below 1e-6, switch to scientific notation. Months and years are Gregorian averages (30.44 and 365.2425 days), so they are not exact calendar spans.
What is the difference between metric and imperial units?
Metric (SI) units such as metres, grams and litres scale by powers of ten and are the standard for science and in most countries. Imperial and US customary units such as feet, pounds and gallons are used mainly in the United States, and the UK uses a mix of both. Exact conversion factors link the two systems.
Is it safe to use an online unit converter, and does it upload my values?
Yes. This unit converter runs in your browser and nothing you type is uploaded; open the Network tab in your browser's DevTools to check. The only thing it remembers is the units you pin in the All Conversions list, saved in your browser's local storage on your own device. Click a pin again to remove it.