MeasurementDB

Base unit; c = 299,792,458 m/s exactly

The metre is the length of the path travelled by light in vacuum in 1/299,792,458 of a second. It was first defined by...

Base unit; h = 6.62607015 × 10⁻³⁴ J·s exactly

The kilogram is defined by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds. Until 20 May 2019 it...

Base unit; caesium-133 frequency = 9,192,631,770 Hz exactly

The second is defined by taking the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom to...

25.4 mm (exact)

The inch is defined as exactly 25.4 millimetres. Britain and the United States agreed this value in the 1959...

0.45359237 kg (exact)

The avoirdupois pound is defined as exactly 0.45359237 kilograms. The figure was chosen in the 1959 agreement as a...

4.54609 L (exact)

The imperial gallon was created by the Weights and Measures Act 1824 as the volume of ten pounds of distilled water...

231 in³ = 3.785411784 L (exact)

The US gallon is defined as 231 cubic inches, exactly 3.785411784 litres. It descends from the English Queen Anne wine...

1852 m (exact)

The international nautical mile is exactly 1852 metres, about 6076 feet. It approximates one minute of latitude, which...

9,460,730,472,580,800 m (exact)

A light-year is the distance light travels in vacuum in one Julian year of 365.25 days, which works out at exactly...

1.602176634 × 10⁻¹⁹ J (exact)

An electronvolt is the energy gained by one electron accelerated through a potential difference of one volt. Since the...

4046.8564224 m² (exact)

The acre is 4840 square yards, one chain by one furlong, exactly 4046.8564224 square metres. It originally represented...

31.1034768 g (480 grains, exact)

The troy ounce is 480 grains, exactly 31.1034768 grams, about 10 per cent heavier than the avoirdupois ounce. Gold...