About this tool
Conversions use standard SI-based formulas. Temperature conversions handle Celsius, Fahrenheit, and Kelvin correctly, including their different zero points. Common conversions supported include cm to inches, kg to lbs, miles to km, and Celsius to Fahrenheit.
How to use the Unit Converter
- Pick a category — length, weight, temperature, or volume.
- Enter a value and choose the "From" unit.
- Choose the "To" unit — the converted result updates instantly.
Common use cases
- Converting a recipe's cups and ounces to metric grams and milliliters
- Checking a package's weight in kilograms against a pounds-based shipping limit
- Converting a room's dimensions from feet to meters for furniture shopping
- Translating a weather forecast between Celsius and Fahrenheit
Worked example
A US recipe calling for 2 cups of flour translates to roughly 473 milliliters by volume — but bakers who weigh ingredients usually want grams instead, and flour's weight-per-cup varies depending on how it's measured (sifted vs. scooped), so a volume-to-weight recipe conversion is always an approximation rather than an exact figure the way length or temperature is. For a cleaner example: converting a checked-bag weight limit of 50 lbs to kilograms gives 22.68 kg — worth checking before an international flight, since many airlines outside the US post limits in kilograms and a small miscalculation can mean a surprise fee at the counter. Temperature works differently again: 100°F is 37.78°C, calculated with an offset-and-scale formula rather than a straight multiplication, because Fahrenheit and Celsius don't share a zero point.
Things to watch out for
Not all "cups" are the same across measurement systems — a US cup (236.6 mL) differs from a metric cup (250 mL) and a UK imperial cup, which matters for precise baking but rarely for everyday conversions. Weight and mass are also often used interchangeably in casual conversation but aren't strictly identical (mass vs. force under gravity) — for any conversion on Earth's surface, though, the distinction won't affect the practical result. When converting temperature, remember 0°C and 0°F are not the same point and neither is a "double the number" shortcut accurate — always use the proper offset formula rather than a rule of thumb for anything beyond a rough mental estimate.
If this tool's answer doesn't quite match another converter you've used, see Why Your Unit Conversion Doesn't Match: Rounding Errors Explained.
Exact definitions behind US customary units
Since the 1959 international yard and pound agreement, US customary units have been defined exactly in metric terms. The US gallon is defined as 231 cubic inches, which fixes every liquid measure. NIST publishes these definitions. This converter uses these exact factors and displays results with up to three decimal places.
| Unit | Exact definition |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 0.3048 m |
| 1 mile | 1,609.344 m |
| 1 pound | 0.45359237 kg |
| 1 ounce | 28.349523125 g |
| 1 US gallon | 3.785411784 L |
| 1 US quart | 0.946352946 L |
| 1 US pint | 0.473176473 L |
| 1 US cup | 236.5882365 mL |
Because the display stops at three decimal places, 1,000 pounds shows as 453.592 kg here, against an exact 453.59237 kg. For lab or engineering work that needs more digits, multiply by the exact definition yourself.
Which cup this converter uses
The Cups option is the US customary cup, 236.5882365 mL (half a US pint). US nutrition labels use a rounded cup of 240 mL, which FDA rules define for serving sizes. For most recipes the 1.4% difference doesn't matter, but it adds up: 4 cups is about 946 mL here, against 960 mL with the label cup. Many metric recipes, such as Australian ones, use a 250 mL cup, which is different again.
Gallons, quarts and tons that share a name
- US vs imperial gallon. The Gallons, Quarts and Pints options here are US measures. The imperial gallon used in the UK is defined as exactly 4.54609 liters, about 20% larger than the US gallon of 3.785411784 liters.
- Metric ton vs short ton. The Ton option is the metric ton, 1,000 kg. The US "short ton" is 2,000 pounds, which is 907.18474 kg, and the UK "long ton" is 2,240 pounds.
- Fluid ounce vs ounce. The Ounces option measures weight (28.349523125 g). A US fluid ounce is a volume, 29.5735295625 mL, and the two only line up for liquids close to the density of water.
For single conversions with a printable chart, see kg to lbs, cm to inches and Celsius to Fahrenheit. The article on unit conversion rounding errors explains why converters can disagree in the last digit.
Frequently asked questions
Yes — the tool uses the exact defined factors (for example, 1 mile = 1609.344 meters and 1 pound = 0.45359237 kilograms exactly; US volume units are based on the 231-cubic-inch gallon). Displayed results are rounded to 6 decimal places.
Temperature scales (Celsius, Fahrenheit, Kelvin) have different zero points, so converting between them requires an offset calculation rather than a simple multiplication factor used for length, weight, or volume.
A US customary cup is exactly 236.5882365 mL, half of a US pint. This converter uses that customary cup. Nutrition labels use a rounded cup of 240 mL. Many metric countries use a 250 mL cup, so check which one a recipe means.
It depends on the ton. A metric ton, also called a tonne, is 1,000 kg, and that is the ton this converter uses. A US short ton is 2,000 pounds, or 907.18474 kg, and a UK long ton is 2,240 pounds, or about 1,016 kg.