How To Convert Imperial Gallon to Gallon
Formula: Multiply the Imperial gallon value by 1.2009499255 to get US gallons.
Example: Convert 7.5 imp gal to gallons.
7.5 × 1.2009499255 = 9.00712444125 gal
To do it by hand, write your Imperial gallons number. Multiply it by 1.2009499255. Keep the same number of decimal places you need. Round at the end, not in the middle, for best accuracy.
Quick Answer
1 imp gal = 1.2009499255 gal
- 2 imp gal = 2.401899851 gal
- 5 imp gal = 6.0047496275 gal
- 10 imp gal = 12.009499255 gal
Conversion Formula
gallons (gal) = imperial gallons (imp gal) × 1.2009499255
Recommended (IAU standard style): Use defined base units, then convert with fixed constants.
1 imp gal = 4.54609 L 1 gal (US) = 3.785411784 L So, 1 imp gal in US gal = 4.54609 ÷ 3.785411784 = 1.2009499255 gal
This means an Imperial gallon is bigger than a US gallon. So when you convert from imp gal to gal, the number goes up.
- Start with the value in imp gal
- Multiply by 1.2009499255
- Round the final answer to the decimals you need
Imperial gallon
An Imperial gallon is a volume unit used in the UK and some Commonwealth contexts. Its symbol is imp gal.
It was standardized in the British Imperial system in the 1800s. Today it is defined exactly as 4.54609 liters, which keeps conversions consistent.
- Measuring fuel in the UK (miles per gallon values historically used imp gal)
- Brewing and beverage production in some regions
- Older engineering and maintenance manuals
- Bulk liquids in agriculture and small industry
- Historical records and trade documents
Gallon
A gallon here means the US liquid gallon, a common US volume unit. Its symbol is gal.
It comes from older English volume measures and was later standardized in the United States. It is defined as exactly 231 cubic inches, equal to 3.785411784 liters.
- Gasoline and diesel sales in the United States
- Water use, pools, and household utility estimates
- Paint, cleaners, and chemical containers
- Food service, syrups, and beverage mixes
- Aquariums and small tanks in US measurements
Is this Conversion of Imperial Gallon To Gallon Accurate?
Yes. This conversion is based on fixed, internationally accepted definitions. The Imperial gallon is defined exactly as 4.54609 L, and the US liquid gallon is defined exactly as 231 in³, which equals 3.785411784 L. Using these exact definitions gives the stable factor 1.2009499255, so results are reliable for school, lab work, engineering estimates, and everyday use. For more details on how we treat standards and rounding, see our accuracy standards.
Real Life Examples
These examples show when you might need to convert imp gal to US gal, and what the numbers look like.
- UK car fuel log used in the US: You recorded 12 imp gal of fuel on a UK-based sheet. In the US that is 12 × 1.2009499255 = 14.411399106 gal.
- Brewing recipe scaled for US containers: A recipe calls for 5 imp gal of water. In US gallons, that is 6.0047496275 gal, so a 6-gallon US kettle is just enough.
- Small rain tank label from the UK: A tank is marked 20 imp gal. In US gallons that is 24.01899851 gal, helpful when matching US pump specs.
- Cleaning concentrate planning: A facility plans to mix 3 imp gal of solution. That equals 3.6028497765 gal in US measurements for US-labeled dosing cups.
- Aquarium water change guide: A guide says change 2 imp gal weekly. That is 2.401899851 gal in the US, so you can measure it with a 1-gallon jug plus 0.401899851 gal more.
- Fuel storage drum tracking: A note says you used 8 imp gal from a drum. That equals 9.607599404 gal in US gallons for US inventory records.
- Farm spray mix conversion: A farm plan calls for 10 imp gal of carrier liquid. In US gallons that is 12.009499255 gal, so you need a larger US tank than 12.0 gal if you want a little extra room.
Quick Tips
- Imperial gallons are larger, so the US gallon number will be bigger after conversion.
- For quick mental math, use imp gal × 1.2 for a close estimate.
- A handy fraction: × 1.2 is the same as × 6 then ÷ 5.
- For better accuracy, keep more decimals during the calculation, then round once at the end.
- If you see “gal” in US contexts, it almost always means US liquid gallon, not Imperial.