Why does it show every unit instead of just the one I asked for?

Because you often do not know which unit you want until you see it. A measurement in metres is more useful shown as feet, inches, yards and miles together than as any single one of them, and it costs nothing to compute them all in your browser.

Why do so many converters get temperature wrong?

Because Celsius and Fahrenheit do not share a zero point. Most conversions are a simple ratio, since a kilometre is always 1,000 metres, but temperature needs a multiplication and an offset. A converter built only on ratios reports 0 °C as 0 °F. This one stores an offset alongside every factor, so the affine cases come out right.

Is a kilobyte 1,000 bytes or 1,024?

Both are listed, because both are in use. A kilobyte (kB) is 1,000 bytes under the SI definition that drive manufacturers use. A kibibyte (KiB) is 1,024 bytes, which is what operating systems usually mean when they say KB. The gap is why a 1 TB drive shows up as about 931 GB.

Are US and imperial measures the same?

Not for volume. A US gallon is 3.785 litres and an imperial gallon is 4.546, about 20% larger. Pints and fluid ounces differ too. Both sets are included and labelled, so recipes and fuel figures do not silently drift.

How precise are the results?

Conversions run in double precision and results are shown to 12 significant digits, which is comfortably inside what a double can represent. Values defined exactly (an inch is exactly 2.54 cm, a mile exactly 1,609.344 m) come back exact rather than as 2.5400000000000005.

Is anything sent to a server?

No. Every conversion is arithmetic that runs in your browser. Nothing is uploaded, and the tool keeps working with no network connection once the page has loaded.

Unit Converter

Convert between units across ten categories, and see every unit in the category at once rather than picking a target first. Temperature is handled as the affine conversion it actually is, so 0 °C comes out as 32 °F and not as zero.

From

To3.28083989501

1 m in every length unit

Millimetremm
1,000
Centimetrecm
100
Kilometrekm
0.001
Inchin
39.3700787402
Footft
3.28083989501
Yardyd
1.09361329834
Milemi
0.000621371192237
Nautical milenmi
0.000539956803456

Quick conversion reference

The conversions people look up most, to the precision that matters. Exact values are legal definitions, not approximations.

From	To	Multiply by	Note
Inches	Centimetres	2.54	Exact by definition
Feet	Metres	0.3048	Exact by definition
Miles	Kilometres	1.609344	Exact by definition
Pounds	Kilograms	0.45359237	Exact by definition
Ounces	Grams	28.349523125	Exact by definition
US gallons	Litres	3.785411784	Exact; the imperial gallon is 4.54609 L
Fluid ounces (US)	Millilitres	29.5735295625	The imperial fl oz is 28.4130625 mL
Acres	Hectares	0.40468564224	Exact by definition
Fahrenheit	Celsius	(°F − 32) × 5/9	Not a multiplier: the scales have different zeros
Celsius	Kelvin	+ 273.15	Offset only; the degree size is identical
Knots	km/h	1.852	Exact; one knot is one nautical mile per hour
PSI	Bar	0.0689475729	1 bar is exactly 100,000 pascals

Common questions

Why does it show every unit instead of just the one I asked for?: Because you often do not know which unit you want until you see it. A measurement in metres is more useful shown as feet, inches, yards and miles together than as any single one of them, and it costs nothing to compute them all in your browser.
Why do so many converters get temperature wrong?: Because Celsius and Fahrenheit do not share a zero point. Most conversions are a simple ratio, since a kilometre is always 1,000 metres, but temperature needs a multiplication and an offset. A converter built only on ratios reports 0 °C as 0 °F. This one stores an offset alongside every factor, so the affine cases come out right.
Is a kilobyte 1,000 bytes or 1,024?: Both are listed, because both are in use. A kilobyte (kB) is 1,000 bytes under the SI definition that drive manufacturers use. A kibibyte (KiB) is 1,024 bytes, which is what operating systems usually mean when they say KB. The gap is why a 1 TB drive shows up as about 931 GB.
Are US and imperial measures the same?: Not for volume. A US gallon is 3.785 litres and an imperial gallon is 4.546, about 20% larger. Pints and fluid ounces differ too. Both sets are included and labelled, so recipes and fuel figures do not silently drift.
How precise are the results?: Conversions run in double precision and results are shown to 12 significant digits, which is comfortably inside what a double can represent. Values defined exactly (an inch is exactly 2.54 cm, a mile exactly 1,609.344 m) come back exact rather than as 2.5400000000000005.
Is anything sent to a server?: No. Every conversion is arithmetic that runs in your browser. Nothing is uploaded, and the tool keeps working with no network connection once the page has loaded.

Conversion factors are the exact legal definitions where one exists. An inch is exactly 2.54 cm and a pound exactly 0.45359237 kg, so those conversions are exact rather than approximate. Temperature uses offsets rather than factors, and that is shown in the working.