Convert Gallons to Liters
Switch US gallons into liters for metric fuel economy (L/100 km), aquarium volumes and metric paint or chemical containers.
1 gal = 3.7854 L
One US liquid gallon equals exactly 3.785411784 litres. To convert US gallons to litres, multiply by 3.785411784 — so 10 gal = 37.85 L and 15 gal = 56.78 L. The imperial gallon used in the UK is a different and larger unit at 4.54609 L, roughly 20 percent bigger, which is the single most important thing to establish before converting. That gap is why fuel economy figures never transfer directly: 30 miles per US gallon is 36 miles per imperial gallon, and quoting the wrong one flatters or penalises a car by a fifth. A rough mental conversion is to multiply by four and subtract five percent — 20 gal gives 80 minus 4, about 76 L against the true 75.7. Note also that the US dry gallon is a third unit at 4.405 L, used for produce, and that a US gallon of water weighs 8.34 lb while an imperial gallon weighs 10 lb.
Quick reference: gallons (us) to liters
| Gallons (US) | Liters |
|---|---|
| 1 | 3.785 L (US) |
| 2 | 7.571 L |
| 5 | 18.927 L |
| 10 | 37.854 L |
| 12 | 45.425 L |
| 15 | 56.781 L |
| 20 | 75.708 L |
| 50 | 189.271 L |
| 100 | 378.541 L |
How do you convert gallons (us) to liters?
Formula: litres = US gallons × 3.785411784 • A 15-gallon car fuel tank → 15 × 3.785411784 = 56.78 L. • A 1-gallon milk jug → 3.785 L, against the 4 L jugs sold in Canada. • 30 US gallons per minute of pump flow → 113.56 L/min. • The same 15 figure in imperial gallons → 15 × 4.54609 = 68.19 L, over 11 L more than the US result.
When and why people use gallons (us) to liters
Fuel is the dominant case. US pumps dispense gallons while nearly everywhere else sells litres, so comparing fuel prices or vehicle range across borders requires converting. Fuel economy compounds the problem because miles per gallon and litres per 100 km are inverse measures — a higher mpg is better while a lower L/100 km is better, so the two cannot be compared by converting the units alone. Aquariums, tanks and pools are the second. Capacity is stated in gallons in US product listings and litres elsewhere, and dosing chemicals or medications by volume makes an accurate conversion necessary rather than optional. Recipes and bulk liquids are the third, particularly in brewing and food production where batch sizes are quoted in gallons in American sources and litres in European ones.
Common mistakes to watch for when converting gallons (us) to liters
The US-versus-imperial gallon distinction causes more errors than anything else. An imperial gallon is 4.54609 L against the US gallon's 3.785411784 L, a 20% difference, so a UK recipe or a Canadian specification using imperial gallons converts to a materially different volume. Second, the US dry gallon is a third unit again at about 4.405 L, used for produce and rarely encountered but capable of producing confusing results. Third, fuel economy conversion is not a unit conversion at all — going from mpg to L/100 km requires the reciprocal relationship 235.215 ÷ mpg, not a multiplication. Finally, US fuel pumps and UK pumps both display a number without always labelling which gallon is meant, so establish the standard before trusting a converted figure.
How to estimate gallons (us) to liters in your head
Multiply by 4 and subtract about 5.5%. For 15 US gallons: 15 × 4 = 60, minus 3.3 gives 56.7 L against a true 56.78. An alternative is to multiply by 3.8, which is close enough for almost everything and easier than carrying the full 3.785411784. For 15 gallons that gives 57 L, a 0.4% overestimate. Anchors: 1 gal ≈ 3.8 L, 5 gal ≈ 19 L, 10 gal ≈ 38 L, 15 gal ≈ 57 L, 20 gal ≈ 76 L. As with the reverse direction, the dominant risk is not arithmetic but unit identity — if the source is British, multiply by 4.55 instead. A 15 imperial gallon figure is 68 L, over 11 L more than the US result, which is the difference between filling a tank and overflowing it.
Gallons (US) to Liters FAQ
How many litres is a US gallon?
- Exactly 3.785411784 L.
Is a UK gallon the same?
- No. The imperial gallon is 4.54609 L, about 20% larger than the US gallon.
How many litres in a 15-gallon fuel tank?
- 56.78 L using US gallons, or 68.19 L if the figure is imperial.
How do I convert mpg to L/100 km?
- It is a reciprocal, not a multiplication: L/100 km = 235.215 ÷ mpg. A 30 mpg car uses about 7.8 L/100 km.
What is a US dry gallon?
- A separate unit of about 4.405 L used for produce. It is not interchangeable with the liquid gallon.
Why do Canadian milk jugs hold 4 L?
- Canada is metric, so containers are sized in round litres rather than converted from gallons. A US gallon jug is 3.785 L.
How many litres per minute is 30 gallons per minute?
- 113.56 L/min using US gallons.
How do I work out cost per litre from a price per gallon?
- Divide the gallon price by 3.785411784. A $4.00 US gallon is about $1.06 per litre, which is how to compare US pump prices against European ones.
Does temperature affect the volume?
- Slightly. Fuel expands as it warms, so a gallon dispensed on a hot afternoon contains marginally less mass than one dispensed at dawn. Retail pumps in most jurisdictions do not compensate for this.
Is my input stored?
- No. The calculation runs entirely in your browser.
Last updated:
Sources: NIST Handbook 44 on US liquid measure; UK Weights and Measures Act defining the imperial gallon as 4.54609 L exactly; NIST Special Publication 811 for fuel-economy conversion.