Gallons to Liters Chart (Aquarium)
Convert common US aquarium gallon sizes to liters and UK gallons. Full chart from 1 to 180 gallons with exact factors for accurate dosing, stocking, and equipment sizing.
Aquarium gear, medications, and fish profiles get written in three different volume units depending on where they come from: US gallons, liters, and UK (imperial) gallons. Mixing them up will throw off your dosing, heater wattage, and stocking. This chart converts every common US tank size into liters and UK gallons using the exact conversion factors, so you can read any source and dose to the right number.
Quick answer: Multiply US gallons by 3.78541 to get liters, and by 0.832674 to get UK (imperial) gallons. A 10 gallon tank is about 37.9 liters (8.3 UK gal), a 55 gallon is about 208 liters (45.8 UK gal), and a 125 gallon is about 473 liters (104 UK gal). Real water volume is usually 85 to 90 percent of these figures once substrate and decor are in. Convert any size with our aquarium unit converter and confirm true volume with the aquarium volume calculator.
Gallons to liters conversion chart
Liters and UK gallons are calculated from US gallons: 1 US gallon = 3.78541 liters and 1 UK gallon = 4.54609 liters. Values are rounded to two decimals. These describe the rated tank volume, not the real water volume after substrate and decor.
| US gallons | Liters (L) | UK (imperial) gallons |
|---|---|---|
| 1 gal | 3.79 L | 0.83 UK gal |
| 2.5 gal | 9.46 L | 2.08 UK gal |
| 5 gal | 18.93 L | 4.16 UK gal |
| 10 gal | 37.85 L | 8.33 UK gal |
| 20 gal | 75.71 L | 16.65 UK gal |
| 29 gal | 109.78 L | 24.15 UK gal |
| 40 gal | 151.42 L | 33.31 UK gal |
| 55 gal | 208.20 L | 45.80 UK gal |
| 75 gal | 283.91 L | 62.45 UK gal |
| 90 gal | 340.69 L | 74.94 UK gal |
| 125 gal | 473.18 L | 104.08 UK gal |
| 150 gal | 567.81 L | 124.90 UK gal |
| 180 gal | 681.37 L | 149.88 UK gal |
The exact conversion factors
There are only a few numbers to remember, and they are exact, not approximate. To convert US gallons to liters, multiply by 3.78541. To go the other way, divide liters by 3.78541, or multiply by 0.264172. The UK gallon is a separate, larger unit: one imperial gallon is 4.54609 liters, which makes one US gallon equal to about 0.832674 UK gallons. That 20 percent gap is exactly why a tank described as "20 gallon" can mean two different water volumes depending on the country.
For quick mental math at the tank, liters divided by 3.8 gives a close US gallon estimate, and US gallons times 3.8 gets you back to liters within a rounding error. Those shortcuts are fine for a sanity check, but use the full factors for anything you dose, like fertilizer or medication, where small percentage errors stack up.
Why liters matter even for US keepers
Plenty of the best aquarium information is written in liters. European fertilizer dosing guides, many fish care sheets, and a lot of planted-tank and reef calculators default to metric. If you keep your tank in gallons but follow a liter-based guide, a clean conversion keeps your dosing honest. The same applies in reverse for keepers outside the US reading American stocking and equipment advice.
Volume drives almost every other decision in the hobby. Heater wattage is sized at roughly 3 to 5 watts per gallon, filter turnover is set at 4 to 10 times the tank volume per hour, and stocking is capped by total water. Get the volume right first, in whatever unit you prefer, and the rest of the numbers fall into place. Our unit converter switches between gallons, liters, and imperial gallons in one step.
Convert to real water volume, not the label
The chart above converts the rated capacity, but your tank holds less than its label once it is set up. You fill below the rim, and gravel, sand, rocks, and driftwood all displace water. Real volume typically lands around 85 to 90 percent of the rating. A "55 gallon" tank that converts to 208 liters on paper often holds closer to 185 liters of actual water.
This is the volume that matters for dosing. Whether you are adding water conditioner, plant fertilizer, or a medication, calculate the dose on real water volume so you do not overtreat or undertreat. Measure your inside dimensions and run them through the volume calculator to get an accurate gallon or liter figure, then convert as needed.
More conversions and planning tools
For standard tank footprints in both inches and centimeters, see our common aquarium dimensions chart. To plan equipment around your converted volume, the full calculators hub covers heater size, filter turnover, stocking, and more, and the reference charts collect every quick-lookup table in one place.
Frequently Asked Questions
How many liters are in a US gallon?
One US gallon equals exactly 3.78541 liters. So a 10 gallon tank holds about 37.9 liters, a 55 gallon holds about 208 liters, and a 125 gallon holds roughly 473 liters. The US gallon is smaller than the UK (imperial) gallon, which is 4.54609 liters, so always confirm which gallon a product or guide means before you convert or dose anything.
What is the difference between a US gallon and a UK gallon?
A UK or imperial gallon is about 20 percent larger than a US gallon. One US gallon is 3.78541 liters while one UK gallon is 4.54609 liters, so a US gallon is only about 0.83 UK gallons. American tanks and equipment are rated in US gallons, while British and some Commonwealth sources use imperial gallons. Mixing the two up will throw off heater wattage, dosing, and stocking math.
Does my tank really hold the rated number of gallons?
Almost never. The printed rating measures the tank filled to the very top rim. In practice you fill an inch or two below the rim, and substrate, rocks, and decor displace several more gallons or liters. Real water volume usually lands around 85 to 90 percent of the label. For accurate dosing and conversions, measure inside dimensions and use our volume calculator instead of trusting the box.
Why does liter dosing matter for fish medication?
Most water conditioners, fertilizers, and medications are dosed per gallon or per liter, and many are sold internationally with liter instructions. If you dose a converted volume based on the tank label rather than real water volume, you can overdose a planted tank or underdose a medication so it fails. Convert to liters, then reduce by about 10 percent for substrate and decor displacement to find your true treatment volume.
How do I convert liters back to US gallons?
Divide liters by 3.78541 to get US gallons. For a quick mental estimate, divide liters by 3.8, or multiply liters by 0.264. So a 100 liter tank is about 26.4 US gallons, and a 200 liter tank is about 52.8 US gallons. To go from liters to UK gallons instead, divide by 4.54609. Our unit converter handles all of these directions instantly.
Is a 200 liter tank a good beginner size?
Yes. A 200 liter tank is roughly 53 US gallons, similar to a standard 55 gallon, which is one of the most forgiving sizes for a first community aquarium. The larger water volume dilutes waste and resists temperature and pH swings, so early mistakes do less harm. Bigger tanks are genuinely easier than nano tanks, so 150 liters or more is a smart starting point if you have the space.
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