Unit
converter.
Convert length, mass, temperature, area, volume, speed and digital storage using exact definitions. See your value in every unit at once, and convert temperature changes as well as temperature readings.
Exact factors,
honest rounding.
- Every factor is an exact definition: 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 US gallon = 231 cubic inches, 1 imperial gallon = 4.54609 L.
- Calculations keep full precision. Only the displayed result is rounded, to the number of significant figures you choose.
- Temperature readings convert with an offset (0 °C = 32 °F). Temperature differences convert by ratio only (a 1 °C change = a 1.8 °F change).
- Temperatures below absolute zero are rejected.
- kB, MB, GB and TB are decimal (1000×). KiB, MiB, GiB and TiB are binary (1024×).
How does unit conversion work?
Each unit is defined as an exact multiple of a base unit, such as the meter or kilogram. To convert, multiply by the size of the source unit and divide by the size of the target unit. A mile is exactly 1,609.344 meters and a kilometer is 1,000 meters, so 1 mile is 1.609344 km.
NIST advises keeping full precision during a calculation and rounding only the final answer. The calculator follows that rule, and the precision setting changes only how many significant figures are displayed.
result = value × (size of source unit ÷ size of target unit)Why are temperatures different?
Celsius and Fahrenheit have different zero points, so converting a reading needs an offset as well as a ratio: °F = °C × 1.8 + 32. That is why 10 °C is 50 °F.
A temperature change has no zero point. If the weather warms by 10 °C, it warms by 18 °F, not 50 °F. Choose Temperature difference for changes, ranges, tolerances and “degrees above ambient”. Converting a difference as if it were a reading is a common source of error.
reading: °F = °C × 9/5 + 32, K = °C + 273.15
difference: Δ°F = Δ°C × 9/5, ΔK = Δ°CWhy is my 1 TB drive only 931 GB?
Drive makers use decimal prefixes: 1 TB is 10¹² bytes. Many operating systems count in binary units of 1,024 and often label them “GB”. In binary, 10¹² bytes is 931.32 GiB. Nothing is missing; the same bytes are counted with two different prefixes. The IEC binary prefixes (KiB, MiB, GiB, TiB) were introduced to remove this ambiguity.
US and imperial volumes are not the same
A US gallon is 3.785411784 L, while an imperial (UK) gallon is 4.54609 L. That is about 20% larger. The fluid ounces differ too: a US fl oz is about 29.57 mL and a UK fl oz about 28.41 mL. Check which system a recipe, fuel figure or product label uses before converting.
For recipes, use the cooking measurement converter: it adds metric, Australian and imperial cups and spoons and breaks awkward amounts into measuring cups and spoons.
Worked examples.
Marathon distance in miles
A marathon is 42.195 km. How many miles is that?
26.218757 miles (26.2 miles is the usual rounded figure).
Load this exampleOven temperature
A recipe asks for an oven at 350 °F. What is that in Celsius?
176.67 °C (most ovens would be set to 175 or 180 °C).
Load this exampleA temperature change
The forecast says it will be 10 °C warmer tomorrow. How much warmer is that in Fahrenheit?
18 °F warmer. Converting it as a reading would wrongly give 50 °F.
Load this exampleDrive capacity
How many gibibytes are in a drive sold as 1 TB?
931.32257 GiB.
Load this exampleFloor area
An apartment is listed at 1,500 square feet. What is that in square meters?
139.35456 m² (exact, because 1 ft² = 0.09290304 m²).
Load this exampleWhat this calculator
does not do.
- It converts between units of the same kind. It cannot convert volume to weight, because that needs the density of the substance. For cooking, use the milligrams to teaspoons calculator.
- Mass units are converted as mass. Pounds and ounces here are avoirdupois, not troy (used for precious metals).
- Area and volume conversions apply to the stated unit only. They do not account for the shape of a room or container.
- Digital storage results are exact counts of bytes. Actual usable space on a drive is also reduced by formatting and the file system.
Common questions.
How many kilometers are in a mile?
Exactly 1.609344 km. A kilometer is about 0.621371 miles.
How do I convert Celsius to Fahrenheit?
Multiply by 1.8 and add 32. For a temperature change, only multiply by 1.8.
Is a kilobyte 1,000 or 1,024 bytes?
In the SI and IEC standards a kilobyte (kB) is 1,000 bytes and a kibibyte (KiB) is 1,024 bytes. Some software still uses “KB” for 1,024.
How accurate are the results?
The factors are exact definitions, and calculations use full double precision (about 15–16 significant digits). The display is rounded to the precision you choose.
- NIST SP 811, Appendix B.8 — factors for units listed alphabetically
- NIST SP 811, Appendix B.9 — factors for units listed by kind of quantity — includes the temperature formulas
- NIST — Unit conversion and rounding guidance
- NIST — Prefixes for binary multiples
- Weights and Measures Act 1985, Schedule 1 (UK) — imperial gallon = 4.54609 cubic decimetres
Every factor is stored as an exact definition and converted through a base unit (meter, kilogram, square meter, milliliter, meter per second, byte, kelvin). Our tests check each factor against its published definition, round trips in both directions, absolute-zero validation, and the difference between temperature readings and differences.