Unit Converter

1 inch is exactly 2.54 cm, and 1 mile is 1.609344 km

Enter a value, pick the unit you have and the unit you want, and the answer appears at once. Below it, the same value is listed in every unit of that category, so you can compare inches, feet, yards and miles without converting again. The converter covers 72 units in eight categories (length, weight, temperature, area, volume, time, speed and data) and works from exact definitions such as 1 in = 0.0254 m, 1 lb = 0.45359237 kg and 1 US gallon = 231 in³, so no rounding error builds up along the way.

This guide explains how the calculation works, lists the definitions, gives common conversions, and covers the cases that most often go wrong: temperature differences, KB versus KiB, US versus UK gallons, and cups and ounces.

How the conversion works

1. Choose a category. Switching categories loads a common unit pair for it and keeps the value you typed.
2. Type a value and choose the units. Commas are read as thousands separators; decimals and negative numbers are accepted.
3. The result appears in large type, together with the one-unit factors in both directions and the formula.
4. The "All units" list shows the same value in every unit of the category. Tap a row to make it the target unit.
5. "Copy result" copies the result and formula. "Copy link" copies an address that stores the category, value and units, so opening it shows the same result.

Every unit except temperature is a fixed multiple of a base unit (meter, gram, square meter, liter, second, meter per second or byte), so the converter computes value × base value of the source unit ÷ base value of the target unit. For inches to centimeters, 1 in = 0.0254 m and 1 cm = 0.01 m, so the factor is 0.0254 ÷ 0.01 = 2.54. Temperature scales start from different zero points, so they use the formulas below instead.

Unit definitions

The inch, foot and pound follow the international yard and pound of 1959. Since January 1, 2023, the United States has retired the U.S. survey foot except for historic and legacy uses and applies the international foot (0.3048 m) everywhere, so the acre here is 43,560 international square feet, or 4,046.8564224 m².

Common conversions

Results follow the same rule as the converter screen (10 significant digits, rounded), which is why 1 oz, defined as exactly 28.349523125 g, shows as 28.34952313 g.

Temperature needs a formula

Celsius and Fahrenheit differ in both their zero point and the size of a degree, so one multiplication is not enough. The formulas are °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9 and K = °C + 273.15. 0 °C is 32 °F and 273.15 K, 100 °C is 212 °F, and the two scales meet at −40. A body temperature of 98.6 °F is 37 °C.

A temperature difference converts differently. If the air warms by 10 °C, it has warmed by 18 °F, not 50 °F. The "A difference of 1 °C" row in the result shows this ratio (1 °C of difference = 1.8 °F = 1 K). Nothing can be colder than absolute zero (−273.15 °C = −459.67 °F = 0 K), so the converter rejects such values.

KB and KiB are different units

Data sizes come in decimal units that grow by 1,000 (kB, MB, GB, TB) and binary units that grow by 1,024 (KiB, MiB, GiB, TiB). The binary names were approved by the International Electrotechnical Commission (IEC) in December 1998. A 1 TB drive holds 10¹² bytes, which is 931.3225746 GiB in binary units. When an operating system or app labels binary values as "GB", a 1 TB drive appears as about 931 GB.

Internet speeds are quoted in bits (Mbps), so divide by 8 to get bytes: 100 Mbps moves 12.5 MB per second.

Gallons, cups and ounces depend on the standard

The same name can mean different amounts. The UK gallon (4.54609 L) is about 20% larger than the US gallon (3.785411784 L). A recipe cup can be the US customary cup of 236.5882365 mL, the 240 mL cup used on US nutrition labels, the 250 mL metric cup or a 200 mL measuring cup, so check which one the recipe uses. The weight ounce (oz, 28.349523125 g) and the US fluid ounce (fl oz, about 29.57 mL) are different units too, and the Indonesian ons is 100 g.

Weight and volume can only be converted with a density. One liter of water weighs about 1 kg, but a cup of flour or rice depends on the ingredient and how it is packed, so this converter does not convert between them.

Common mistakes

• Treating a temperature difference as a temperature: a rise of 10 °C is a rise of 18 °F, not 50 °F.
• Counting 1 GB as 1,024 MB: GB and MB step by 1,000. Steps of 1,024 belong to GiB and MiB.
• Mixing up US and UK gallons: converting a UK figure as if it were US gallons understates it by about 17%.
• Confusing ounces and fluid ounces: oz is weight and fl oz is volume. Even for water, 1 fl oz weighs a little more than 1 oz.
• Reading a knot as a mile per hour: 1 kn = 1.852 km/h = 1.150779448 mph.
• Rounding factors early: round once, at the end. Dividing by 2.2 instead of using the exact pound factor puts 150 lb at 68.18 kg instead of 68.0388555 kg.
• Using average months for calendar dates: the month and year here are averages. For the real number of days between two dates, use a date calculator.

Limitations

• Results show 10 significant digits. When the whole-number part is longer, all of its digits are shown (up to 15), and the rest is rounded. Values of 10¹⁵ or more, or below 0.000001, use scientific notation.
• Calculations use the browser's double-precision numbers, so they do not suit work that needs more than 15 digits of precision.
• Months and years are averages; leap seconds and daylight saving time are ignored.
• Conversions that need more than a definition, such as weight to volume, currencies, or clothing and shoe sizes, are not covered.
• Your values are not sent to a server. They are kept only in the page address.

Reference date Definitions were checked on 2026-10-07. Unit definitions do not change from year to year.

Sources

• 01NIST SP 811 — Appendix B.8 Factors for units listed alphabeticallySI conversion factors for the inch, pound, gallon, knot and more
• 02NIST — U.S. Survey FootInternational foot (0.3048 m) applies from 2023-01-01
• 03BIPM — The International System of Units (SI Brochure)Celsius–kelvin relation; hectare, nautical mile and other non-SI units
• 04NIST — Prefixes for binary multiplesKiB, MiB and GiB binary prefixes (IEC, December 1998)
• 05eCFR — 21 CFR 101.9 Nutrition labeling of food1 cup = 240 mL for nutrition labeling
• 06UK Weights and Measures Act 1985 — Schedule 1UK gallon = 4.54609 L

Frequently asked questions

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