What is Imperial gallon?

An Imperial gallon is a volume unit used in the United Kingdom equal to approximately 4.546 litres. It is larger than the US gallon and is commonly referenced for fuel efficiency (miles per gallon) in the UK.

Real-world uses

Imperial gallons are used in the United Kingdom, Canada (for some purposes), and several Caribbean countries. British fuel economy was historically quoted in miles per Imperial gallon. Older Commonwealth-era recipes and industrial specifications may reference Imperial gallons.

History

The Imperial gallon was established by the British Weights and Measures Act of 1824 as the volume occupied by 10 pounds of water at 62°F (≈ 17°C). It replaced several older gallon definitions including the wine gallon (retained by the US) and the ale gallon.

Common mistakes

Assuming the Imperial gallon equals the US gallon. The Imperial gallon is about 4.546 litres versus 3.785 litres for the US gallon. Converting mpg figures between the two systems without adjusting for gallon size gives misleading results.

What is US fluid ounce?

A US fluid ounce is a volume unit equal to approximately 29.57 millilitres. It is used in the United States for beverage servings, cooking measurements, and product labelling.

Real-world uses

US fluid ounces are used for beverage labelling (a standard can of soda is 12 fl oz), cooking measurements, and cosmetics packaging in the United States. Cocktail recipes and bartending rely heavily on fluid ounce measurements (a standard shot is 1.5 fl oz).

History

The US fluid ounce derives from the English wine gallon tradition. When the US and UK diverged in measurement standards in the 19th century, their fluid ounces ended up slightly different. The US fluid ounce is defined as 1/128 of a US gallon.

Common mistakes

Confusing US fluid ounces with Imperial fluid ounces—they differ by about 4% (US: 29.57 mL, Imperial: 28.41 mL). Also, confusing fluid ounces (volume) with avoirdupois ounces (weight), which are completely different measurements.

When is this conversion used?

Converting Imperial gallon to US fluid ounce is useful in the volume domain when comparing values across different measurement standards or applying formulas that require a specific unit.

Worked examples

1 Imperial gallon = 153.72159046 US fluid ounce

1 US fluid ounce = 0.02957353 litre

How to convert Imperial gallon to US fluid ounce

To convert Imperial gallon to US fluid ounce, multiply the value by 153.72159046.

To convert US fluid ounce back to Imperial gallon, multiply by 0.00650527.

Measurement standards

The cubic metre is the SI derived unit of volume. The litre, equal to exactly one cubic decimetre (0.001 m³), is accepted by the BIPM for use alongside SI units. Both the lowercase "l" and uppercase "L" are approved symbols for the litre.

Did you know?

An Olympic swimming pool holds 2,500 cubic metres of water — about 2.5 million litres. The Amazon River discharges roughly 209,000 cubic metres per second, enough to fill 84 Olympic pools every single second.

Quick reference: Imperial gallon to US fluid ounce

Imperial gallonUS fluid ounce
0.115.37215905
0.576.86079523
1153.72159046
2307.44318093
5768.60795232
101,537.21590465
253,843.03976162
507,686.07952323
10015,372.15904646
25038,430.39761616
50076,860.79523231
1,000153,721.59046462

Common values

Imperial gallonUS fluid ounce
A teaspoon0.00109985 Imperial gallon0.16907011 US fluid ounce
A cup of coffee0.05499231 Imperial gallon8.45350568 US fluid ounce
A water bottle0.10998462 Imperial gallon16.90701135 US fluid ounce
A bathtub65.99077449 Imperial gallon10,144.20681055 US fluid ounce
A swimming pool (Olympic)549,923.12074772 Imperial gallon84,535,056.7546075 US fluid ounce

Available Volume units

More Imperial gallon conversions