Are the gallons and cups US or UK measures?

They're US customary units: a US gallon is 3.785 L, a US cup is 236.6 mL, and a US fluid ounce is 29.57 mL. An imperial (UK) gallon is 4.546 L, about 20 percent larger, so adjust when following a British recipe or reading a UK fuel figure.

Why does temperature work differently from the other units?

Celsius, Fahrenheit, and Kelvin each start counting from a different zero, so converting between them needs an offset, not just a multiplication. That's why 0 C becomes 32 F rather than 0 F. The converter applies the proper affine formulas instead of a plain ratio.

How accurate are the conversions?

They use the internationally defined exact factors, such as 1 inch = 2.54 cm, 1 lb = 0.45359237 kg, and 1 mile = 1609.344 m, rather than rounded approximations. Because linear categories convert through a base unit, a round trip like mi to km back to mi returns exactly what you started with.

Which categories and units are included?

Six categories: length (mm, cm, m, km, in, ft, yd, mi), weight (mg, g, kg, t, oz, lb), volume (mL, L, m3, tsp, tbsp, fl oz, cup, pt, qt, gal), area (up to acre and hectare), speed (m/s, km/h, mph, knot, ft/s), and temperature (C, F, K).

Can I type into either field?

Yes. Both fields are live, so you can convert in whichever direction you're thinking and the other updates instantly. A swap button flips the from and to units in one click.

Unit Converter

Convert length, weight, temperature, volume, area, and speed units instantly.

From

Conversions are computed locally in your browser.

What is Unit Converter?

Unit Converter switches between length, weight, temperature, volume, area, and speed units instantly — cm to inches, kg to pounds, Celsius to Fahrenheit, and more. Pick a category, choose your units, and type in either field; the other updates live.

Key features

Six categories: length, weight, temperature, volume, area, speed
Type in either field — both stay in sync
Swap units with one click
Handles temperature correctly (not a simple ratio like the others)

How to convert between units correctly

The Unit Converter switches between everyday measurement units instantly and entirely in your browser. It covers six categories, each with the units you actually reach for:

Length — mm, cm, m, km, in, ft, yd, mi
Weight — mg, g, kg, t (metric tonne), oz, lb
Volume — mL, L, m³, tsp, tbsp, fl oz, cup, pt, qt, gal
Area — mm², cm², m², km², in², ft², yd², acre, hectare
Speed — m/s, km/h, mph, knot, ft/s
Temperature — °C, °F, K

Steps

Pick a category.
Choose your units in the "from" and "to" dropdowns.
Type a value. Either field accepts input and the other updates live, so you can convert in whichever direction you're thinking. The swap button flips the two units in one click.

Why temperature is handled differently

Every other category converts by a single multiplication: 1 inch is always exactly 2.54 cm, whether you have 1 inch or 1,000. Temperature doesn't work that way. Celsius, Fahrenheit, and Kelvin each start counting from a different zero point, so converting between them means shifting by an offset and scaling — an affine formula, not a plain ratio. That's why 0 °C becomes 32 °F (not 0 °F), and why the naïve "just multiply" approach that's fine for length or weight gives the wrong answer for temperature. The converter uses the proper formulas (e.g. °F = °C × 9⁄5 + 32, K = °C + 273.15), so the offsets are always applied.

The volume gotcha: these are US units

The volume units here are US customary, which matters because the same name means different amounts around the world. A US gallon is 3.785 L, but an imperial (UK) gallon is 4.546 L — about 20% larger. Likewise a US cup is 236.6 mL, not the 250 mL metric cup used in a lot of recipes, and a US fluid ounce is 29.57 mL. If you're following a British recipe or reading a UK fuel figure, adjust for the imperial difference; converting "gallons" blindly will be off by a fifth.

A note on precision

Conversion factors use the internationally defined exact values rather than rounded approximations — 1 inch = 2.54 cm exactly, 1 lb = 0.45359237 kg exactly, 1 mile = 1609.344 m — so results stay accurate even for very large numbers. Linear categories convert through a base unit (meter, kilogram, liter, square meter, meter per second), which keeps every pair consistent: converting mi → km → mi returns exactly what you started with. A couple of everyday anchors worth memorizing: 1 kg is 2.2046 lb, 1 mi is 1.609 km, and a comfortable 20 °C room is 68 °F. The weight category's t is the metric tonne (1000 kg), not the US short ton or the UK long ton, so double-check which "ton" a spec sheet means before trusting it.

Everything runs locally — nothing you type is ever sent anywhere.

Frequently asked questions

Are the gallons and cups US or UK measures?: They're US customary units: a US gallon is 3.785 L, a US cup is 236.6 mL, and a US fluid ounce is 29.57 mL. An imperial (UK) gallon is 4.546 L, about 20 percent larger, so adjust when following a British recipe or reading a UK fuel figure.
Why does temperature work differently from the other units?: Celsius, Fahrenheit, and Kelvin each start counting from a different zero, so converting between them needs an offset, not just a multiplication. That's why 0 C becomes 32 F rather than 0 F. The converter applies the proper affine formulas instead of a plain ratio.
How accurate are the conversions?: They use the internationally defined exact factors, such as 1 inch = 2.54 cm, 1 lb = 0.45359237 kg, and 1 mile = 1609.344 m, rather than rounded approximations. Because linear categories convert through a base unit, a round trip like mi to km back to mi returns exactly what you started with.
Which categories and units are included?: Six categories: length (mm, cm, m, km, in, ft, yd, mi), weight (mg, g, kg, t, oz, lb), volume (mL, L, m3, tsp, tbsp, fl oz, cup, pt, qt, gal), area (up to acre and hectare), speed (m/s, km/h, mph, knot, ft/s), and temperature (C, F, K).
Can I type into either field?: Yes. Both fields are live, so you can convert in whichever direction you're thinking and the other updates instantly. A swap button flips the from and to units in one click.

Privacy

Every conversion is local arithmetic in your browser; the numbers you enter are never sent to a server.