Convert litres, US gallons and Imperial gallons without mixing up the units.
Open live calculator →100 litres equals about 26.4 US gallons or 22 UK gallons.
Aquarium brands and care guides use different volume systems. This converter returns all three values from one input.
The live tool updates immediately and shows the result in the units commonly used by aquarium keepers around the world.
Check whether a product label means US or UK gallons.
Keep litres visible when comparing international equipment.
Round only after the conversion is complete.
The US gallon is defined as 3.785 litres, while the Imperial gallon used historically in the UK and Commonwealth countries is 4.546 litres—about 20% larger. The difference comes from different historical definitions: the US kept the old English wine gallon while Britain redefined its gallon in 1824. For aquarium keepers this matters constantly, because American products, forums and care guides dominate the hobby online while much of the world measures in litres.
Products manufactured for the North American market—filters rated "for tanks up to 40 gallons", water conditioners dosed "per 10 gallons"—virtually always mean US gallons. UK retailers today usually list litres, but older British aquarium books and some hobbyist forums still use Imperial gallons. If a source does not say which gallon it means, its origin is the best clue: American sources mean US gallons.
When you chain conversions—litres to gallons for a dosing chart, then gallons back to litres for a bucket—rounding at each step compounds the error. Convert with full precision and round only the final number you act on. For dosing sensitive medications, work in litres directly whenever the label allows it, since litres are the unit your measuring jug most likely shows.
One US gallon is 3.785 litres. To convert gallons to litres, multiply by 3.785; to convert litres to US gallons, multiply by 0.264.
One Imperial gallon is 4.546 litres, about 20% more than a US gallon. Multiply litres by 0.22 to get Imperial gallons.
A 55 US gallon tank is about 208 litres of geometric capacity, and the real water volume is lower still once substrate, décor and the air gap are subtracted. Nothing is wrong—the marketing size is gross capacity in US gallons.