Unit Converter
Convert between metric and imperial units across eight categories, with exact conversion factors and results as you type.
Common conversions
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About the Unit Converter
Two measurement systems in daily use means constant conversion. A recipe in cups, an oven in Fahrenheit, a running app in kilometres, a parcel in pounds, a screen in inches and a road sign in miles — most people move between systems several times a day without noticing, and each crossing is a chance to be wrong.
The errors are not always harmless. NASA lost the Mars Climate Orbiter in 1999 because one team supplied thrust data in pound-force seconds while the software expected newton-seconds. Medication dosing errors from pound-to-kilogram confusion are a recognised patient safety issue. A cooking conversion that is 10% out will not hurt anyone, but it will ruin a cake.
This converter covers eight categories: length, weight and mass, temperature, area, volume, speed, digital storage and time. The factors used are the exact definitional ones — an inch is exactly 25.4 millimetres, a pound is exactly 0.45359237 kilograms — rather than the rounded approximations that accumulate error across multi-step conversions. Temperature is handled separately because it needs an offset as well as a scale factor.
How to use it
- Choose a categoryLength, weight, temperature, area, volume, speed, data or time.
- Enter a valueType into either field — conversion runs in both directions automatically.
- Select your unitsPick the source and target units from the lists for that category.
- Read the resultThe converted value appears as you type, with sensible precision for the magnitude involved.
- Swap if neededOne click reverses the direction of the conversion.
- See the common conversionsA reference table of frequently used conversions for the selected category.
Features
- Eight categoriesLength, weight and mass, temperature, area, volume, speed, digital storage and time.
- Exact factorsDefinitional conversion constants rather than rounded approximations, so multi-step conversions stay accurate.
- BidirectionalType in either field and the other updates — no need to decide direction first.
- Correct temperature mathsCelsius, Fahrenheit and Kelvin handled with proper offsets, not a bare multiplier.
- Binary and decimal data unitsBoth KB (1000 bytes) and KiB (1024 bytes) available, since the distinction genuinely matters.
- Reference tablesCommon conversions listed for each category so you can sanity-check the result.
Who uses this tool
- CookingConvert a recipe between grams, ounces and cups, and oven temperatures between Celsius and Fahrenheit.
- TravelRead distances in miles or kilometres, temperatures in either scale, and luggage limits in kilograms or pounds.
- DIY and constructionMove between metric and imperial measurements when materials and plans use different systems.
- Developers and ITConvert between bytes, kilobytes, mebibytes and gigabytes with the binary and decimal distinction handled properly.
Tips worth knowing
- Storage vendors sell in decimal gigabytes (1000³ bytes) while operating systems often report binary gibibytes (1024³) — this is why a 1 TB drive shows as roughly 931 GB.
- Fluid ounces differ between the US and the UK, and so do pints and gallons. Check which system a recipe or spec means before converting.
- For quick mental estimates: kilometres to miles is roughly multiply by 0.6, and Celsius to Fahrenheit is double it and add 30.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32. So 20°C becomes 68°F. Going the other way, subtract 32 and multiply by 5/9. Temperature conversion needs the offset because the two scales have different zero points, unlike length or weight.
What is the difference between KB and KiB?
A kilobyte (KB) is 1,000 bytes under the decimal SI convention; a kibibyte (KiB) is 1,024 bytes under the binary convention. The gap widens with scale, which is why a drive sold as 1 TB is reported by many operating systems as about 931 GB. Both are offered here.
Are US and UK measurements the same?
Not for volume. A US fluid ounce, pint and gallon are all smaller than their imperial equivalents — a US gallon is about 3.79 litres against the imperial 4.55. Length and weight units are identical between the two systems.
How accurate are the conversions?
They use the exact definitional factors: an inch is precisely 25.4 mm, a pound precisely 0.45359237 kg. Results are displayed at a sensible precision for the magnitude, with more decimal places retained internally than shown.
What is the difference between mass and weight?
Mass is the amount of matter, measured in kilograms; weight is the force gravity exerts on it, measured in newtons. In everyday use the terms are interchangeable because gravity is effectively constant on Earth, and this converter follows the everyday convention.
Can I convert between area and volume units?
No — they measure different dimensions and no conversion exists between them. Square metres measure area and cubic metres measure volume; converting between them requires a third measurement, such as a depth.