Unit Conversions Calculators
Millimeters to inches, kilograms to pounds, milliliters to ounces: the conversions everyone reaches for, each with the exact factor, the formula worked with your number, a reference table, and honest rounding.
Length & Height 6
- CM to Feet ConverterCentimetres to feet and inches, said the way people say it.
- CM to Inches ConverterCM to inches with a full chart, formula, and worked steps.
- MM to Inches ConverterMM to inches: decimal and nearest 16th, with the rounding shown.
- Inches to CM ConverterInches to cm, fractions accepted, with a full chart and formula.
- Inches to Feet ConverterInches to feet, decimal and feet-and-inches, with a full chart.
- Meters to Feet ConverterMeters to feet with decimal and feet-inches results, plus a chart to 100 m.
Weight 3
Volume & Kitchen 6
- Liters to Gallons ConverterBoth gallons every time, because they differ by twenty percent.
- Ounces to Cups ConverterFluid ounces are exact. Weight ounces depend on the ingredient.
- ML to Oz Converterml to oz (US) with a bottle-size chart and a swap toggle.
- Cups to Grams ConverterCups to grams, by ingredient: flour, sugar, butter, honey and more.
- Cooking Measurement ConverterCups, tablespoons, teaspoons, fl oz, ml, liters: any unit to any other.
- Oven Temperature ConverterFahrenheit, Celsius, gas mark, and the fan adjustment, all from one number.
Area 1
More tools 4
- Bra Size CalculatorYour US, UK, and EU bra size plus sister sizes, minus the judgment.
- Coordinates ConverterPaste any GPS format, get all three, with 4,000 year old arithmetic shown.
- Gold CalculatorMelt value by weight and karat, plus what buyers actually pay.
- Radians to Degrees CalculatorRadians to degrees and back, exact when you type pi, with the working shown.
Which converter do you need?
- Length, small. mm to inches, cm to inches, inches to cm, and inches to feet.
- Length, larger. meters to feet, and the height converter when you want feet and inches from centimetres, which is the version people actually want for a person's height.
- Weight. kg to lbs and lbs to kg, or the weight converter for stones, ounces, and grams in one place.
- Volume. ml to oz for liquids, and the cooking measurement converter for kitchen units.
- Kitchen crossovers. cups to grams and the oven temperature converter sit in both this category and cooking, because that is where people look for them.
These factors are exact, not approximate
An inch is exactly 25.4 millimetres. Not roughly, not to five decimal places: exactly, by international agreement since 1959, which is when the US, UK, and other Commonwealth countries reconciled slightly different national inches into one definition. A pound is exactly 0.45359237 kilograms by the same agreement.
This matters because it means any error you see is a rounding decision, not a limitation of the conversion. Our converters use the exact defined factors and then tell you where they rounded and by how much, rather than starting from a shortened factor and compounding it. If you need the full definitions, they are published by NIST and we link them on each page.
Where rounding actually bites
Fractions are the usual culprit. Converting to the nearest sixteenth of an inch is what a tape measure can show you, but it is not exact, and on a long run those sixteenths accumulate. We show the fraction and the exact decimal together, plus the size of the rounding error, so you can decide whether it matters for what you are building. For a bookshelf it does not. For a cabinet run against a wall, it does.
The other place to be careful is fluid ounces, which are not the same in the US and the UK. An imperial fluid ounce is about 4 percent smaller than a US one, and a pint differs by considerably more. Recipes written on different sides of the Atlantic quietly disagree about both.
Frequently asked questions
How many cm are in an inch?
Exactly 2.54 centimetres, which is 25.4 millimetres. This is a defined value rather than a measured one, agreed internationally in 1959 to reconcile slightly different national inches. Any imprecision you encounter comes from rounding the result, not from the conversion factor itself.
Why do your answers differ slightly from another converter?
Almost always rounding. Some converters start from a shortened factor such as 2.5 or round intermediate steps, which compounds the error. We use the exact defined factors and round only at the end, and we show you the size of the rounding error. If the difference is larger than that, check whether one of the tools is using imperial rather than US units.
Are US and UK fluid ounces the same?
No. An imperial fluid ounce is roughly 4 percent smaller than a US fluid ounce, and the pints differ by more than that because they contain different numbers of ounces. This is a real source of recipe failure when a British recipe meets an American measuring jug or the reverse.
Why does converting to fractions introduce error?
Because a fraction like a sixteenth of an inch is a rounding target, not an exact equivalent of a metric value. It is the right answer for a tape measure and the wrong one for a long cumulative run, where those roundings add up. We show the nearest fraction, the exact decimal, and the error between them so the choice is yours.