Aquarium sizes, product labels and dosing instructions don't always use the same unit. US tanks are sold in US gallons, European tanks in litres, and older UK guides use imperial gallons. Here's how they relate.
US gallons, UK gallons and litres
- 1 US gallon = 3.785 litres (231 cubic inches)
- 1 UK gallon = 4.546 litres, about 1.2 US gallons
- 1 litre = 0.264 US gallons, or 0.22 UK gallons
So to convert, multiply US gallons by 3.785 for litres, or divide litres by 3.785 for US gallons. The aquarium volume converter does it instantly.
Conversion chart
US gallon tanks in litres
| Tank | Litres | UK gallons |
|---|---|---|
| 5 gallon | 19 L | 4.2 UK gal |
| 10 gallon | 38 L | 8.3 UK gal |
| 20 gallon | 76 L | 16.7 UK gal |
| 20 gallon long | 76 L | 16.7 UK gal |
| 29 gallon | 110 L | 24.1 UK gal |
| 30 gallon | 114 L | 25.0 UK gal |
| 40 gallon breeder | 151 L | 33.3 UK gal |
| 50 gallon | 189 L | 41.6 UK gal |
| 55 gallon | 208 L | 45.8 UK gal |
| 60 gallon | 227 L | 50.0 UK gal |
| 75 gallon | 284 L | 62.5 UK gal |
| 90 gallon | 341 L | 74.9 UK gal |
| 100 gallon | 379 L | 83.3 UK gal |
| 125 gallon | 473 L | 104.1 UK gal |
Common litre sizes in gallons
| Litres | US gallons | UK gallons |
|---|---|---|
| 25 L | 6.6 US gal | 5.5 UK gal |
| 54 L | 14.3 US gal | 11.9 UK gal |
| 60 L | 15.9 US gal | 13.2 UK gal |
| 100 L | 26.4 US gal | 22.0 UK gal |
| 112 L | 29.6 US gal | 24.6 UK gal |
| 125 L | 33.0 US gal | 27.5 UK gal |
| 180 L | 47.6 US gal | 39.6 UK gal |
| 200 L | 52.8 US gal | 44.0 UK gal |
| 240 L | 63.4 US gal | 52.8 UK gal |
| 300 L | 79.3 US gal | 66.0 UK gal |
| 450 L | 118.9 US gal | 99.0 UK gal |
Why European tank sizes look different
European aquariums are designed in centimetres and sold in litres, so their sizes don't line up with US gallon tanks. A 60 litre tank, often around 60 x 30 x 35 cm, is about 16 US gallons. A 240 litre tank is about 63 US gallons. If your tank was sold in litres, measure it and use the aquarium volume calculator in centimetres.
Which number to use for dosing
Follow the unit on the product label and convert your tank's real water volume into it. Remember that real water volume is lower than the tank's nominal size; the real water volume calculator accounts for substrate, decor and the gap below the rim.
Frequently asked questions
How many litres is a 55 gallon tank?
A 55 US gallon tank holds about 208 litres. In UK gallons that's about 46.
Is a UK gallon bigger than a US gallon?
Yes. A UK (imperial) gallon is 4.546 litres and a US gallon is 3.785 litres, so a UK gallon is about 20% bigger.
How do I convert litres to gallons?
Divide litres by 3.785 for US gallons, or by 4.546 for UK gallons. For example, 200 litres is about 53 US gallons.