Definition:Imperial/Volume/Gallon

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Definition

The (imperial) gallon is an imperial unit of volume.

It is defined as the volume of $10$ pounds of water under a specific set of conditions.


Conversion Factors

\(\ds \) \(\) \(\ds 1\) imperial gallon
\(\ds \) \(=\) \(\ds 2\) pottles
\(\ds \) \(=\) \(\ds 4\) quarts
\(\ds \) \(=\) \(\ds 277 \cdotp 4198\) cubic inches
\(\ds \) \(=\) \(\ds 0 \cdotp 1605\) cubic feet
\(\ds \) \(=\) \(\ds 4 \, 546 \cdotp 09\) millilitres
\(\ds \) \(=\) \(\ds 4 \cdotp 54609\) litres
\(\ds \) \(=\) \(\ds 4 \cdotp 54609 \times 10^{-3}\) cubic metres


Symbol

$\mathrm {gal}$

The symbol for the (imperial) gallon is $\mathrm {gal}$.


Its $\LaTeX$ code is \mathrm {gal} .


Also known as

The imperial gallon is also known as the UK gallon in order specifically to distinguish it from the US gallon.

Sources which are of British origin, particularly earlier ones, may refer to this unit merely as the gallon, assuming an understanding by their audience that the gallon is the imperial gallon by default.


Also see


Historical Note

Prior to $1824$, there existed a number of different gallons throughout the British Empire.


The imperial gallon was defined in $1824$ as a volume close to the ale gallon.

Its original definition was the volume of $10$ pounds (approximately $4.5$ kilograms) of distilled water, weighed in air with brass weights with the barometer standing at $30$ inches of mercury ($102$ kilopascals) at a temperature of $62$ degrees Fahrenheit ($17$ degrees Celsius).


In $1963$, the imperial gallon was redefined as the volume of $10$ pounds of distilled water of density $0 \cdotp 998859$ grams per millilitre weighed in air of density $0 \cdotp 001217$ grams per millilitre against weights of density $8 \cdotp 136$ grams per millilitre.

This works out to be $4.546096$ litres or $277.4198$ cubic inches.


The imperial gallon was redefined once again in $1985$ to be exactly $4 \cdotp 54609$ litres by the Weights and Measures Act.


Sources