📏 Unit Converter

📐 Category

🔁 Units

From

📝 Value

📤 Result

🎯 Converted value

{{ result.fromValue }} {{ result.fromUnit }} → {{ result.toUnit }}

⚠️

ℹ️ About Unit Converter

What does this tool do?

The Unit Converter converts a numeric quantity between any two units inside a single physical category — for example metres to feet, kilograms to pounds, kilowatt-hours to joules, or degrees Celsius to Fahrenheit. The conversion factors come from the United States National Institute of Standards and Technology Special Publication 811 (NIST SP 811), the BIPM SI brochure, and the international yard and pound agreement of 1959 where applicable.

Categories and base units

Length — base unit metre. Includes mm, cm, m, km, in, ft, yd, mile, nautical mile, light-year, astronomical unit.
Mass — base unit kilogram. Includes mg, g, kg, lb, oz, metric ton, stone, grain, short ton.
Volume — base unit litre. Includes mL, L, m³, cm³, US gallon, imperial gallon, US quart/pint/fl oz/cup/tbsp/tsp, imperial fl oz.
Area — base unit square metre. Includes cm², m², km², hectare, ft², in², yd², acre, mi².
Energy — base unit joule. Includes J, kJ, calorie, kilocalorie, watt-hour, kWh, BTU, eV, foot-pound.
Power — base unit watt. Includes W, kW, MW, metric horsepower (PS), mechanical horsepower, BTU/h, ft·lb/s.
Pressure — base unit pascal. Includes Pa, kPa, MPa, bar, atm, psi, torr, mmHg, inHg.
Temperature — formula-based via kelvin: Kelvin, Celsius, Fahrenheit, Rankine.
Speed — base unit metre per second. Includes m/s, km/h, mph, ft/s, knot, Mach (sea level approximation).

How the conversion works

Each non-temperature unit declares a multiplicative "to-base" factor that expresses one unit of the listed item in the category's base unit. Converting from unit A to unit B in the same category is then:

out = value × factor_A / factor_B

Temperature is special because the scales do not share a common zero point, so the tool normalises every input to kelvin first and converts back from kelvin to the output scale. The exact formulas used are:

K = °C + 273.15
°C = (°F − 32) × 5/9
K = °Ra × 5/9

Sample conversions

Category	Input	Output	Reference
Length	1 mi	1609.344 m	Exact (NIST SP 811 §B.8)
Length	1 nmi	1852 m	Exact (international nautical mile)
Mass	1 lb	0.45359237 kg	Exact (1959 yard & pound agreement)
Volume	1 gal (US)	3.785411784 L	Exact (231 in³)
Volume	1 gal (UK)	4.54609 L	Exact (UK 1985 W&M Act)
Area	1 acre	4046.8564224 m²	Exact (43560 ft²)
Energy	1 cal	4.184 J	Exact (thermochemical calorie)
Energy	1 kWh	3,600,000 J	Exact
Pressure	1 atm	101325 Pa	Exact (NIST SP 811)
Temperature	0 °C	273.15 K	Formula
Temperature	100 °C	212 °F	Boiling point of water (1 atm)
Speed	1 mph	0.44704 m/s	Exact (1609.344 / 3600)

References

NIST SP 811 — Guide for the Use of the International System of Units: nist.gov/pml/special-publication-811 (download PDF: physics.nist.gov/cuu/pdf/sp811.pdf).
BIPM — The International System of Units (SI) Brochure: bipm.org/en/publications/si-brochure.
International Yard and Pound Agreement (1959) — defines the exact value 1 yd = 0.9144 m and 1 lb = 0.45359237 kg.
IAU 2012 Resolution B2 — defines 1 au = 149,597,870,700 m exactly.

Privacy note: the interactive converter runs in your browser. The public API endpoint executes the same compiled TypeScript module on the server, so values you submit through the API are sent over the network.

API Usage Example:

POST /api/tools/math/unit-converter
Content-Type: application/json

{
    "category": "length",
    "fromUnit": "mi",
    "toUnit": "km",
    "value": 1
}