How this calculator works
An ordinary unit becomes memorable when it is compared with a familiar object. A football field is a convenient length of about 91 metres, and a blue whale is a convenient mass of about 150 tonnes. These comparisons are deliberately approximate: a bus is not exactly 4.4 metres, an elephant varies, and a bathtub holds whatever its shape allows. The regular units use exact definitions, while the object units use one round value each. For temperature, no object is a linear unit, so the page instead shows the reading in Celsius, Fahrenheit and kelvin and names the closest reference point.
Formula
base value = entered value x F(unit), where F is the size of the input unit in the family base unit (metre, kilogram, second, square metre, metre per second, cubic metre, joule or watt). The value in another unit is base ÷ F(that unit). Temperature is converted with the usual degree offsets, not a ratio.
Worked example
One football field is 91.44 m, 0.09144 km, 300 ft or about 20.8 double-decker buses. One blue whale is 150,000 kg or 25 African elephants. One Olympic swimming pool is 2,500 m3, or about 16,667 bathtubs.
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Frequently asked questions
Are the object sizes exact?
No. They are single round values chosen to make a comparison easy. A football field has fixed markings, but a bus, an elephant and a bathtub vary by model or individual, and the page says so rather than implying precision.
Why is temperature handled differently?
A temperature scale has an arbitrary zero and a degree size, so there is no such thing as twice room temperature. The page converts the reading properly and compares it with reference points instead of dividing one temperature by another.
Which unit families are covered?
Length, mass, time, area, speed, volume, energy, power and temperature. It is a broad selection rather than an exhaustive catalogue, and the regular units in each family are the ones most people meet day to day.