UK Gallons To US Gallons Converter
Convert imperial UK gallons to US gallons, litres and fluid ounces for fuel economy, water tanks, brewing, aquariums and imported specifications.
Convert Gallons
Converted Volume
10 UK gallons converts to about 12.01 US gallons.
UK Gallon And US Gallon Difference
An imperial UK gallon is exactly 4.54609 litres. A US liquid gallon is exactly 3.785411784 litres. Because the UK gallon is larger, one UK gallon equals about 1.20095 US gallons. The reverse is also important: one US gallon is about 0.83267 UK gallons.
This difference matters in fuel economy and tank sizes. UK miles per gallon and US miles per gallon are not directly comparable because the gallon size changes. A car listed at 40 UK mpg is not the same as 40 US mpg. Convert the gallon system before comparing numbers.
Formula And Method
Litres = UK gallons x 4.54609.
US gallons = litres / 3.785411784.
US gallons = UK gallons x 1.20095042.
UK gallons = US gallons x 0.83267418.
UK gallons = litres / 4.54609.
UK To US Gallon Table
| UK Gallons | US Gallons | Litres | Practical Note |
|---|---|---|---|
| 1 | 1.20 | 4.55 | Single imperial gallon. |
| 5 | 6.00 | 22.73 | Small container check. |
| 10 | 12.01 | 45.46 | Default example. |
| 20 | 24.02 | 90.92 | Larger water or fuel amount. |
| 50 | 60.05 | 227.30 | Tank planning value. |
Where Gallon Confusion Happens
1Fuel Economy
UK mpg uses imperial gallons. US mpg uses US gallons. Convert before comparing imported vehicle data.
2Water Tanks
Tank labels may come from UK, US or metric suppliers. Litres are the safest shared unit.
3Brewing And Recipes
Beer, syrup and batch recipes can shift strength or yield if the wrong gallon system is used.
Worked Examples
10 UK Gallons
10 x 4.54609 = 45.4609 litres. Divide by 3.785411784 and the result is 12.01 US gallons.
20 US Gallons
20 x 3.785411784 = 75.708 litres. Divide by 4.54609 and the result is 16.65 UK gallons.
Fuel MPG Check
To compare fuel economy, convert the gallon system or use L/100km. L/100km avoids UK versus US gallon confusion.
Precision Notes
For fuel and engineering, keep at least two decimals or convert through litres. For home brewing or aquarium work, litres are often easier because dosing, water changes and equipment ratings commonly use metric volumes. For casual garden water estimates, one decimal may be enough.
Do not use this page for dry gallons or historical local measures. It covers the modern UK imperial gallon and modern US liquid gallon only. If a source is old, regional or agricultural, check its definition before converting.
Related Gallon And Litre Conversions
| Starting Volume | Metric Equivalent | Other Gallon System | Best Use |
|---|---|---|---|
| 1 UK gallon | 4.54609 L | 1.20095 US gal | Imperial fuel or older UK container. |
| 1 US gallon | 3.785411784 L | 0.83267 UK gal | Imported US label. |
| 5 UK gallons | 22.73045 L | 6.00475 US gal | Water carrier or small batch. |
| 5 US gallons | 18.92706 L | 4.16337 UK gal | US bucket or brewing kit. |
| 10 UK gallons | 45.4609 L | 12.0095 US gal | Default converter value. |
| 10 US gallons | 37.85412 L | 8.32674 UK gal | Tank or aquarium note. |
| 20 UK gallons | 90.9218 L | 24.019 US gal | Large water storage. |
| 20 US gallons | 75.70824 L | 16.6535 UK gal | US appliance capacity. |
| 50 UK gallons | 227.3045 L | 60.0475 US gal | Fuel or tank planning. |
| 50 US gallons | 189.2706 L | 41.6337 UK gal | Imported tank specification. |
UK Gallons In Fuel, Brewing And Tank Specs
Fuel economy is the place where the gallon difference causes the most expensive mistakes. UK mpg uses miles per imperial gallon. US mpg uses miles per US liquid gallon. Because the UK gallon is larger, a UK mpg number will look higher than the US mpg value for the same vehicle and fuel use. If you are comparing cars, convert both figures to L/100km or use the correct gallon system before making a cost comparison.
Brewing, aquarium and tank specifications have a different problem: equipment may be sold by a US brand, a UK supplier or a metric manufacturer. A “10 gallon” vessel can mean about 45.46 litres if imperial, or about 37.85 litres if US liquid. That gap is large enough to affect recipe strength, salt dosing, water treatment, headspace and pump sizing. Litres are the safest shared unit for instructions, labels and purchase notes. The converter result is therefore specific because it keeps UK gallons, US gallons and litres visible at the same time.
For imported manuals, look for clues around the number. US manuals may pair gallons with quarts, cups or Fahrenheit. UK or older Commonwealth material may mention imperial gallons, pints or miles per gallon. Metric equipment will usually give litres first. If the document does not say which gallon it means, avoid guessing for fuel, chemical dosing, brewing gravity, aquarium treatment or storage capacity. Convert both possible gallon systems to litres and compare the difference before buying parts or mixing a batch.
For records, write the converted litre value beside the original figure. A note such as “12 US gallons, 45.4 L” is easier to check later than a bare gallon number. It also helps when a fuel, water or brewing worksheet is shared with someone in another country. Keep the original unit name as part of the note.
FAQ
How many US gallons are in 1 UK gallon?
1 UK gallon is about 1.20095 US gallons.
How many litres are in a UK gallon?
1 UK gallon is exactly 4.54609 litres.
How many litres are in a US gallon?
1 US liquid gallon is exactly 3.785411784 litres.
Is UK mpg the same as US mpg?
No. The gallon size differs, so the same mpg number does not mean the same fuel use.
Should I use litres instead?
For cross-country comparison, litres are often clearer.
Does this cover dry gallons?
No. It covers UK imperial gallons and US liquid gallons.
Sources
- National Institute of Standards and Technology. (2008). Guide for the Use of the International System of Units. NIST. https://www.nist.gov/pml/special-publication-811
- International Bureau of Weights and Measures. (2019). The International System of Units (SI), 9th ed. BIPM. https://www.bipm.org/en/publications/si-brochure
- GOV.UK. (n.d.). Weights and measures: the law. GOV.UK. https://www.gov.uk/weights-measures-and-packaging-the-law