The conversion factors
1 US gallon = 3.785411784 liters (exactly, 231 cubic inches)
1 UK (imperial) gallon = 4.54609 liters (exactly)
So 1 liter is about 0.2642 US gallons or 0.2200 UK gallons. A UK gallon is roughly 20% larger than a US gallon, which matters when a tank or a product label comes from a UK source.
Common tank sizes
- 10 US gal = 37.9 L
- 20 US gal = 75.7 L
- 29 US gal = 109.8 L
- 40 US gal = 151.4 L
- 55 US gal = 208.2 L
- 75 US gal = 283.9 L
Advertised size vs. real water volume
Tank sizes are nominal. Glass thickness, the rim and the water level below the top mean the real water volume is usually 5–15% smaller. Use the aquarium volume calculator to compute it from your measurements, and use that figure for dosing and water changes.
Frequently asked questions
How many liters is a 55 gallon aquarium?
A 55 US gallon tank is about 208.2 liters (55 × 3.785). A 55 UK gallon tank would be about 250 liters.
How many US gallons is 100 liters?
100 liters is about 26.4 US gallons (100 ÷ 3.785).
Are US and UK gallons the same?
No. A UK (imperial) gallon is 4.546 liters, about 20% more than a US gallon (3.785 liters). US sources almost always mean the US gallon.
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