Unit converters
Each conversion uses a factor fixed by SI or by a legal definition (inch, pound). Temperature goes through kelvin so the scales stay consistent.
US and UK units do not always match: the US gallon and the UK gallon differ. The converters say which one, rather than showing an ambiguous “gallon”.
Most used
- Length converterEvery value goes through the meter, then to the target unit. The inch is 25.4 mm exactly since the 1959 agreement, as in the NIST SI conversion factors.
- Weight (mass) converterEveryday speech says “weight”; SI speaks of mass. Conversion goes through the kilogram. The pound (lb) is 0.45359237 kg exactly, a NIST factor, not a weighing on Earth.
- Temperature converterCelsius and Fahrenheit are offset; you do not multiply a “degree” like a meter. Every conversion goes through kelvin. Below 0 K there is no thermodynamic temperature.
- Area converterFactors are SI areas and the international acre. A hectare is 10,000 m² exactly. The acre used here is not the arpent, nor a local survey acre.
Subcategories
Length, mass, area, volume
Linear factors to an SI unit, then to the target unit.
Pressure, energy, power
Pascal, bar and psi; joule, kWh and calorie; watt and horsepower.
Durations and angles
Seconds, hours and weeks; degrees, radians and gradians.
Full list
- Length converterEvery value goes through the meter, then to the target unit. The inch is 25.4 mm exactly since the 1959 agreement, as in the NIST SI conversion factors.
- Weight (mass) converterEveryday speech says “weight”; SI speaks of mass. Conversion goes through the kilogram. The pound (lb) is 0.45359237 kg exactly, a NIST factor, not a weighing on Earth.
- Temperature converterCelsius and Fahrenheit are offset; you do not multiply a “degree” like a meter. Every conversion goes through kelvin. Below 0 K there is no thermodynamic temperature.
- Area converterFactors are SI areas and the international acre. A hectare is 10,000 m² exactly. The acre used here is not the arpent, nor a local survey acre.
- Volume converterThe liter is 1 dm³, or 0.001 m³ exactly. The US gallon and the UK imperial gallon are not the same capacity: the tool separates them, with no ambiguous “gallon” option.
- Speed converterEvery speed routes through the metre per second. 1 km/h is exactly 1/3.6 m/s, and a knot is one nautical mile (1,852 m) per hour, not a statute mile.
- Data storage converterThe maths routes through the bit. Decimal prefixes (1 kB = 1,000 bytes) and binary ones (1 KiB = 1,024 bytes) are handled separately, as IEC 80000-13 specifies.
- Pressure converterEvery pressure routes through the pascal, the SI unit equal to one newton per square metre. The bar is exactly 100,000 Pa and the standard atmosphere 101,325 Pa.
- Energy converterEvery energy routes through the joule. A kilowatt-hour is exactly 3.6 million joules, and a food kilocalorie 4,184 joules.
- Power converterEvery power routes through the watt. Metric horsepower is 735.49875 W and mechanical horsepower 745.7 W: two different units sharing one everyday name.
- Duration converterEvery duration routes through the second. Months and years are deliberately absent: their length varies, unlike the week, which is always 604,800 seconds.
- Angle converterEvery angle routes through the radian, the SI unit. A half turn is π radians, 180 degrees or 200 gradians: three ways of describing the same opening.
Questions
Is the inch rounded?
No. Since 1959, 1 inch = 25.4 mm exactly. The avoirdupois pound is 0.45359237 kg exactly.