Unit Converter

Length, weight, temperature & more

How it works

Select a category using the pills above, choose your units, then type in either field. The result updates instantly in both directions. Use the swap button to reverse the conversion.

Length

The metre is the SI base unit of length, originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. Today it is defined by the fixed speed of light. Common metric units: mm (÷1,000), cm (÷100), km (×1,000).

Imperial length units grew from everyday references: an inch approximated a thumb width, a foot was literally a human foot, a yard the distance from nose to outstretched fingertip, and a mile came from the Roman mille passuum: 1,000 double paces.

1 in = 2.54 cm

1 ft = 12 in = 30.48 cm

1 yd = 3 ft = 0.9144 m

1 mi = 1,760 yd = 1.60934 km

1 m = 3.28084 ft = 1.09361 yd

1 km = 0.621371 mi

Weight

The kilogram is the SI base unit of mass, defined since 2019 by fixing Planck's constant. Common metric units: mg (÷1,000,000), g (÷1,000), metric tonne (×1,000).

Imperial units: the ounce and pound trace back to Roman and medieval trade weights. The stone (14 lb) remains common in the UK for body weight.

1 g = 1,000 mg

1 kg = 1,000 g

1 t = 1,000 kg

1 oz = 28.3495 g

1 lb = 16 oz = 453.592 g

1 stone = 14 lb = 6.35029 kg

1 kg = 2.20462 lb

Temperature

Celsius sets 0 °C at water's freezing point and 100 °C at its boiling point (at standard pressure). Fahrenheit uses 32 °F and 212 °F for the same points; it predates Celsius and remains common in the US. Kelvin is the SI unit; it uses the same degree size as Celsius but starts at absolute zero (-273.15 °C), so there are no negative values.

°F = (°C × 9/5) + 32

°C = (°F - 32) × 5/9

K = °C + 273.15

°C = K - 273.15

Time

The second is the SI base unit of time, defined since 1967 by the oscillation of caesium-133 atoms (exactly 9,192,631,770 cycles per second). All other time units are derived from it.

1 ms = 0.001 s · 1 μs = 0.000001 s · 1 ns = 0.000000001 s

1 min = 60 s

1 hr = 60 min = 3,600 s

1 day = 24 hr = 86,400 s

1 week = 7 days

1 avg month = 30.4375 days (365.25 / 12)

1 avg year = 365.25 days = 8,766 hr

Area

Area is length squared. The SI unit is the square metre (m²). A hectare (ha) is 10,000 m², the standard unit for land in most of the world. An acre is the traditional English land unit, originally the area a yoke of oxen could plough in a day.

1 km² = 1,000,000 m²

1 ha = 10,000 m² = 0.01 km²

1 acre = 4,046.86 m² = 0.404686 ha

1 ft² = 0.0929 m²

1 yd² = 9 ft² = 0.8361 m²

1 km² = 247.105 acres

1 mi² = 640 acres = 2.58999 km²

Volume

The SI unit of volume is the cubic metre (m³), but the litre (1 dm³ = 0.001 m³) is the everyday metric unit. US customary volume units (cup, pint, quart, gallon) differ from their UK imperial counterparts.

1 L = 1,000 mL · 1 m³ = 1,000 L

1 US fl oz = 29.5735 mL

1 US cup = 8 fl oz = 236.588 mL

1 US pt = 2 cups = 473.176 mL

1 US qt = 2 pt = 946.353 mL

1 US gal = 4 qt = 3.78541 L

1 UK fl oz = 28.4131 mL · 1 UK gal = 4.54609 L

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