gal (imp) US customary / imperial
Measures: Volume — how much space
Imperial gallon
The UK gallon — bigger than the US one.
VolumeHow it's defined
Defined in 1985 as exactly 4.54609 litres. UK fuel economy figures still use it, which is why UK and US "mpg" numbers never match.
1 imp gal = 4.54609 L — exact≈ 1.2 US gallons
Convert — honestly
gal (imp) equals
4.54609 L
Litre · factor exact — the base unit for this page
1.20094993 gal (US)
US gallon · factor exact — exact by definition (231 in³)
Conversions run through the litre using the stated factors — no rounding beyond display precision, and every factor says whether it's exact or measured.
Where you meet it
- UK fuel-economy figures
- Old recipes and pub measures trace back to it
Other ways to measure volume
Source
This page is an authored summary of the authoritative definition — checkable one click away.
NIST Special Publication 811 — Guide for the Use of the SI