Unit Converter
Pick a category, type a value and choose two units to convert between metric, US customary and imperial measures — length, mass, temperature, volume, area and speed. Every result shows the factor or formula behind it. Free, no sign-up.
Category
base unit: meter
Result
0.393701 in
1 cm = 0.393701 in
Common length conversions
| From | To |
|---|---|
| 1 in | 2.54 cm |
| 1 ft | 0.3048 m |
| 1 yd | 0.9144 m |
| 1 mi | 1.60934 km |
| 1 m | 3.28084 ft |
| 100 km | 62.1371 mi |
How to Use the Unit Converter
- 1. Choose a category. Length, mass, temperature, volume, area or speed. Each category has its own list of units, and a small note under the buttons names the base unit it converts through.
- 2. Enter a value. Negative numbers and decimals work. The tool opens on 1 cm → inches, so the first result is already on screen.
- 3. Pick the two units. Use From and To, or press Swap to reverse them. Changing the category resets the pair to a sensible default, such as km/h → mph for speed.
- 4. Read the result. The answer is shown to six significant digits, with the factor used (
1 cm = 0.393701 in) or, for temperature, the formula. The table underneath lists six common conversions for the category.
How the Conversions Work
Every unit is stored as an exact multiple of one base unit — meter, kilogram, liter, square meter or meter per second. To convert, the tool multiplies your value by the from unit's factor and divides by the to unit's factor: result = value × factor(from) ÷ factor(to). Going through a base unit means two units never need a direct pairing, and the factor shown in the result is simply the ratio of the two.
Most of the factors are exact by definition, not measured. The international yard and pound agreement of 1959 fixed the inch at 2.54 cm and the pound at 0.45359237 kg, and NIST SP 811 lists the rest. The table gives the definitions behind the less obvious ones.
| Unit | Exact definition |
|---|---|
| Inch, foot, yard, mile | 1 in = 0.0254 m; 1 ft = 0.3048 m; 1 yd = 0.9144 m; 1 mi = 1609.344 m |
| Ounce, stone | 1 oz = 1/16 lb = 28.349523125 g; 1 st = 14 lb = 6.35029318 kg |
| US gallon, quart, pint, cup | 1 gal = 231 in3 = 3.785411784 L; a quart is 1/4 gal, a pint 1/8 gal, a cup 1/16 gal |
| US tablespoon, teaspoon | 1 tbsp = 1/2 US fl oz = 14.78676478125 mL; 1 tsp = 1/3 tbsp |
| Acre | 1 acre = 43,560 ft2 = 4046.8564224 m2 (international foot) |
| Knot | 1 nautical mile per hour, with 1 nautical mile = 1852 m exactly |
| Hectare | 1 ha = 10,000 m2 |
Temperature is the exception. Celsius, Fahrenheit and Kelvin have different zero points, so there is no single factor. The tool converts through Celsius with the standard formulas — °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9 and K = °C + 273.15 — and prints the one it used.
Worked Examples
| Convert | Result | How it works out |
|---|---|---|
| 5 ft to m | 1.524 m | 5 × 0.3048 — exact |
| 70 mph to km/h | 112.654 km/h | 70 × 1.609344 = 112.65408, shown to six digits |
| 2 cups to ml | 473.176 ml | 2 × 236.5882365, a US cup |
| 1 ha to acres | 2.47105 acres | 10,000 ÷ 4046.8564224 |
| 12 oz to g | 340.194 g | 12 × 28.349523125 = 340.1942775 |
| 72 °F to °C | 22.2222 °C | (72 − 32) × 5/9 |
Converting a temperature difference?
The formulas above convert a reading. A rise of 10 °C is a rise of 18 °F, not 50 °F — for differences, multiply by 9/5 and skip the 32.
Common Mistakes
- US versus imperial volume. The cup, pint, quart and gallon here are US customary. A UK imperial gallon is exactly 4.54609 L, about 20% larger than the US gallon, so a UK recipe or fuel figure will not match. Length, mass, area and speed units are the same in both systems.
- Rounded kitchen measures. US nutrition labels use a rounded 240 mL cup, while the exact US customary cup is 236.588 mL. For cooking the difference rarely matters; for lab or dosing work, use millilitres directly.
- Weight versus mass. Pounds, ounces and stone are units of mass here, converted to kilograms. They are not forces, so the tool does not apply gravity.
Which Tool Do You Need?
This converter covers the six everyday categories. For other quantities use a specialist page: Energy Unit Converter for joules, calories, kWh and BTU, Pressure Unit Converter for pascals, bar, atm and psi, Data Storage Converter for bytes, KB versus KiB and transfer times, Metric Prefix Converter for kilo, milli, micro and the other SI prefixes, Angle Converter for degrees and radians, and Light-Year Converter for astronomical distances. To chain several factors and cancel units step by step, use the Dimensional Analysis Calculator.
Frequently Asked Questions
- How do I convert centimeters to inches?
- Divide by 2.54, because an inch is defined as exactly 2.54 cm. So 1 cm is 0.393701 in, and 6 ft (182.88 cm) comes back as 72 in. In the tool, choose Length, enter the value and pick cm → in.
- How do I convert Celsius to Fahrenheit?
- Multiply by 9/5 and add 32: °F = °C × 9/5 + 32. Body temperature, 37 °C, is 98.6 °F; water boils at 100 °C, which is 212 °F. The two scales meet at −40, where both read the same.
- Are the gallons, cups and pints US or imperial?
- US customary. A US gallon is 3.785411784 L, while a UK imperial gallon is 4.54609 L. The UK pint, about 568 mL, is also larger than the US pint at about 473 mL. This tool has no imperial volume units.
- How precise are the results?
- Results are displayed to six significant digits, so 1 mile is shown as 1.60934 km rather than the exact 1.609344. The underlying factors are exact wherever the definition is exact, so the rounding is only in the display.
- Which units are missing, and what does the tool not check?
- The converter sticks to the units listed in each category: for volume that is millilitres, litres, teaspoons, tablespoons, cups, pints, quarts and gallons, and for mass milligrams to tonnes plus ounces, pounds and stone. Anything else, such as energy or pressure, has its own converter. A temperature below absolute zero (0 K, −273.15 °C or −459.67 °F) is not converted: the converter shows a warning instead.
- How many milliliters are in a cup?
- A US customary cup is 236.588 mL, because it is 8 US fluid ounces of 29.5735 mL. Nutrition labels round this to 240 mL, and the metric cup used in Australia and New Zealand is 250 mL, so match the cup to the recipe's country.
- Does it work offline, and is anything sent to a server?
- Conversions run entirely in your browser, and nothing you type is uploaded. Once the page has loaded, the converter keeps working without a connection.