Unit Converter

How it works

This converter covers six categories — length, weight, volume, temperature, area, and speed — each with its own fixed list of units. Picking a category resets the "from" and "to" selectors to that category's units, so you always convert between compatible things (you can't accidentally convert kilograms to kilometers).

For five of the six categories, converting is a straight-line calculation: every unit has a fixed factor relative to a base unit for that category (meters for length, kilograms for weight, liters for volume, square meters for area, meters per second for speed), so converting from unit A to unit B is value × factorA / factorB. All of these factors are exact, standard definitions, not estimates:

• Length uses the meter as its base. 1 inch = 0.0254 m, 1 foot = 0.3048 m, 1 yard = 0.9144 m, and 1 mile = 1609.344 m — all exact, from the 1959 international yard-and-pound agreement.
• Weight uses the kilogram. 1 pound = 0.45359237 kg exactly (same 1959 agreement), and 1 ounce is 1/16 of that — the everyday avoirdupois ounce, not the troy ounce used for precious metals.
• Volume uses the liter, and this is where unit mix-ups happen most: a US gallon (3.785411784 L) and a UK/imperial gallon (4.54609 L) are genuinely different units, about 20% apart, so this tool keeps them as separate entries rather than merging them.
• Area uses the square meter, and its factors are simply the length factors squared — 1 square foot is 0.3048² = 0.09290304 m², and 1 acre (43,560 sq ft) works out to exactly 4046.8564224 m².
• Speed uses meters per second. 1 km/h = 1000/3600 m/s, 1 mph = 0.44704 m/s exactly, and 1 knot = 1852/3600 m/s (one international nautical mile per hour).

Temperature is the exception, because Celsius, Fahrenheit, and Kelvin don't share a common zero point — converting between them needs an offset, not just a multiplication. This tool always converts through Celsius as an intermediate step: it first converts your input to Celsius (subtracting 32 and scaling by 5/9 for Fahrenheit, or subtracting 273.15 for Kelvin), checks that the result isn't below absolute zero (-273.15°C), then converts from Celsius to whatever unit you asked for.

Examples

Length. 100 centimeters converts to exactly 1 meter, and 1 meter converts to about 39.37 inches (39.37007874015748, to be precise, since the inch factor is an exact but non-round number).

Weight. 1 kilogram is about 2.2046 pounds (2.2046226218487757). Going the other way, 1 pound is exactly 0.45359237 kg — and since there are 16 ounces in a pound, 16 ounces also converts to exactly 0.45359237 kg.

Temperature. 0°C is 32°F and 273.15 K (the freezing point of water); 100°C is 212°F and 373.15 K (boiling point). -40° is the one temperature where Celsius and Fahrenheit read the same number: -40°C = -40°F.

Area. 1 square kilometer is 1,000,000 square meters, and 1 hectare is 10,000 square meters — so a hectare is a hundredth of a square kilometer. 1 acre works out to about 4046.86 square meters.

Speed. 100 km/h is about 62.14 mph (62.1371192237334). 10 knots is 18.52 km/h exactly, since a knot and a km/h are both defined in terms of meters per second.

Things to watch for

• US and UK gallons (and cups) are different units, not a rounding choice. If you're converting a US recipe or a US fuel-economy figure, use "gal (US)"; for a UK recipe or spec sheet, use "gal (UK)." Picking the wrong one silently gives a result that's off by about 20%.
• Temperature can't go below absolute zero. Entering a Kelvin value below 0, a Celsius value below -273.15, or a Fahrenheit value below -459.67 returns an error rather than a nonsensical negative-Kelvin result.
• This is a general-purpose, everyday converter, not a certified or legal measurement tool. For customs declarations, engineering drawings, or other contexts that require a certified unit conversion, use the specific standard or software your field requires — the values here are correct, exact SI/international definitions, but this tool doesn't produce a signed or certified conversion record.
• Very large or very small numbers are rejected past ±10¹⁵, and quantities (everything except temperature) can't be negative — there's no such thing as -5 kilometers or -2 liters.
• Everything runs in your browser. No number you enter is sent to a server; the conversion happens locally on your device.