Convert Imperial Gallons to US Gallons
1 imperial gallon (gal (imp)) equals 1.200949926 US gallons (gal (US)).
1 gal (imp) = 1.200949926 gal (US)
Type in either box. Scientific notation works: 1.5e-3.
Converting a list? Use the bulk imperial gallon to US gallon converter to paste a column from Excel.
How to Convert Imperial Gallon to US Gallon
- 1 gal (imp) = 1.200949926 gal (US)
- 1 gal (US) = 0.8326741846 gal (imp)
- Example: convert 15 gal (imp) to gal (US): 15 gal (imp) = 15 × 1.200949926 gal (US) = 18.01424888 gal (US)
Formula
gal (US) = gal (imp) × 1.200949925505
Derivation from SI units:
- 1 imp gal = 4.54609 L = 0.00454609 m³ (exact, by definition)
- 1 US gal = 231 in³ = 231 × (0.0254 m)³ = 0.003785411784 m³
- 1 gal (imp) = 0.00454609 m³ ÷ 0.003785411784 m³ per gal (US) = 1.200949925505 gal (US)
Both units are defined exactly, so the factor is exact. Imperial Gallon definition: imperial gallon; US Gallon definition: US gallon.
Worked examples
- 1 gal (imp) equals 1.200949926 gal (US).
1 gal (imp) × 1.200949926 = 1.200949926 gal (US) - A 12 gal (imp) tank holds 14.41139911 gal (US).
12 gal (imp) × 1.200949926 = 14.41139911 gal (US)
Imperial Gallon to US Gallon conversion table
| Imperial Gallons (gal (imp)) | US Gallons (gal (US)) |
|---|---|
| 0.25 gal (imp) | 0.3002374814 gal (US) |
| 0.5 gal (imp) | 0.6004749628 gal (US) |
| 1 gal (imp) | 1.200949926 gal (US) |
| 2 gal (imp) | 2.401899851 gal (US) |
| 5 gal (imp) | 6.004749628 gal (US) |
| 10 gal (imp) | 12.00949926 gal (US) |
| 15 gal (imp) | 18.01424888 gal (US) |
| 20 gal (imp) | 24.01899851 gal (US) |
| 25 gal (imp) | 30.02374814 gal (US) |
| 40 gal (imp) | 48.03799702 gal (US) |
| 50 gal (imp) | 60.04749628 gal (US) |
| 100 gal (imp) | 120.0949926 gal (US) |
| 1000 gal (imp) | 1200.949926 gal (US) |
Where it's used
UK volumes are converted to US gallons for American buyers, manuals and fuel comparisons.
Imperial Gallon to other volume units
| Conversion | 1 gal (imp) equals |
|---|---|
| imperial gallon to cubic meter | 0.00454609 m³ |
| imperial gallon to liter | 4.54609 L |
| imperial gallon to milliliter | 4546.09 mL |
| imperial gallon to cubic centimeter | 4546.09 cm³ |
| imperial gallon to cubic foot | 0.1605436532 ft³ |
| imperial gallon to cubic inch | 277.4194328 in³ |
| imperial gallon to US gallon | 1.200949926 gal (US) |
Frequently asked questions
How many US gallons are in an imperial gallon?
1 imperial gallon = 1.200949926 gal (US).
How many US gallons are in 1 imperial gallon?
1 gal (imp) = 1.200949926 gal (US).
How do I convert imperial gallons to US gallons?
Multiply the value in gal (imp) by 1.200949926. For example, 15 gal (imp) × 1.200949926 = 18.01424888 gal (US).
Is the gal (imp) to gal (US) conversion exact?
Yes. Both units are defined exactly, so the ratio is exact; its decimal form does not terminate and is shown here to 10 significant figures (more with the precision selector).
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "gallon [Canadian and U.K. (Imperial)]".
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "gallon [U.S.] (gal)".
- NIST Handbook 44, Appendix C: General Tables of Units of Measurement, National Institute of Standards and Technology , Appendix C.
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Convert Imperial Gallons to US Gallons. Retrieved October 17, 2026, from https://scientificconverters.com/volume/imperial-gallons-to-us-gallons/
IEEE
Scientific Converters, "Convert Imperial Gallons to US Gallons," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/volume/imperial-gallons-to-us-gallons/