Unit Converter - Metric, Imperial, Cooking & Fuel

Conversion by a factor

Every category except temperature; in fuel economy, only between two distance-per-fuel units

Result

the converted value

Value

the number you typed

From

the size of one From unit in the category’s base unit (meter, kilogram, liter…)

To

the size of one To unit in the same base unit

Each unit holds one factor to its category’s base unit, so a pair’s factor is the ratio of two. "How it works" prints that factor for your pair to 12 significant digits. The arithmetic runs at full double precision; the Decimals setting rounds only what is shown.

Source: Uses the method in NIST SP 811, Appendix B [1]: multiply by the factor, divide to go back, and build a derived unit’s factor from its parts.

Where the factors come from

Length, area, volume, weight, speed, flow, pressure, energy, power and force

Each factor is a definition from the sources below: the inch is 0.0254 m, the pound 0.45359237 kg and the US gallon 231 cubic inches. 72 of the units match a row of NIST SP 811’s table at its printed digits. Metric sizes use the SI prefixes. The mile, acre and furlong use the international foot of exactly 0.3048 m; the US survey foot was retired at the end of 2022.

Source: NIST SP 811, Appendix B.8 [2] and Chapter 5 [3]; NIST Handbook 44, Appendix C [4]; the SI prefixes as NIST lists them [5].

Energy units

Energy

The small calorie and the food Calorie are the thermochemical calorie, 4.184 J, and a thousand of it; the International Table calorie is 4.1868 J. The BTU is the International Table BTU, and the therm the US therm. The electron volt is 1.602176634 × 10⁻¹⁹ J, exact since 2019.

Source: NIST SP 811, Chapter 5 [3], Appendix B.8 [2] and its footnotes 9 and 24 [1]; the electron volt: [6].

Data and data rates

Data and data transfer rate

A byte is 8 bits. KB, MB, GB and the rest are powers of ten (1 MB is 1,000,000 bytes), as the SI prefixes always are. KiB, MiB, GiB, TiB and PiB are powers of two (1 MiB is 1,048,576 bytes), the binary names that BIPM points to IEC 80000-13 for.

Source: The byte as NIST’s glossary defines it [7]; the SI prefixes and the binary names: BIPM [8] and NIST [9].

Year and month

Time

Year (365.25 days) is the Julian year, 31,557,600 s, a hundredth of the Julian century NIST uses for the light-year; a calendar year of 365 days is 0.07% shorter. Decade, century and millennium are multiples of it. Month (avg., 30.4375 days) is a twelfth of that year.

Source: The Julian century: NIST SP 811, Appendix B, footnote 18 [1]. The average month is CalcTrail’s own; no publisher.

Cooking measures

Volume

The US cup is 8 US fluid ounces, about 236.6 ml, and the US tablespoon and teaspoon are exact fractions of it. The metric tablespoon (15 ml) and teaspoon (5 ml) are the sizes the FDA uses for nutrition labels, which also use a 240 ml cup. The metric cup (250 ml) and the stick of butter (half a US cup) follow a widely used convention.

Source: NIST Handbook 44 [4]; the FDA’s labeling rule [10]. The metric cup and the stick of butter: widely used; no primary source found.

Temperature scales

Temperature

A reading is converted through degrees Celsius. A value below absolute zero is refused. A change converts by the size of a degree alone: 1 °C is 1 K; 1 °F or 1 °R is 5/9 K.

Source: Uses the formulas in NIST SP 811, Appendix B.8 [2]; changes follow its section 8.5 [11].

Gas Mark

Temperature

Mark

the Gas Mark, above 0

The first line holds from Mark 1 up, the second below it (½ is 250 °F, ¼ is 225 °F). Marks below ¼ carry the same halving rule on, CalcTrail’s own extension. Mark 4 is 350 °F, about 176.7 °C; printed charts round the Celsius figure.

Source: Widely used; no primary source found. Searched for a Gas Council, British Standards or government definition of the marks.

Fuel economy

Fuel economy, between L/100 km and a distance per fuel

Result

the converted value

Value

the number you typed

K

235.214583333 for US mpg, 282.480936332 for UK mpg, 100 for km/L

More miles per gallon is fewer liters per 100 km, so the relation is inverse. K is 100 × liters per gallon ÷ kilometers per mile (US gallon 3.785411784 L, UK gallon 4.54609 L, mile 1.609344 km). NIST rounds the US figure to 235.215. Between two distance-per-fuel units the factor rule above applies.

Source: Uses the relation in NIST SP 811, Appendix B.5 [1].

Display rounding

Auto shows up to four decimals from 1 to 999, two from 1,000, none from a million, about four significant figures below 1, and exponential form from 10^15 up and below 10^-9. The Decimals setting caps the places at 2, 4, 6 or 8. It rounds by decimals, not by the significant digits of the value you typed.

Source: CalcTrail’s own display rule; no publisher. NIST SP 811 rounds by significant digits instead (Appendix B.7.2) [1].