Direct answer
Converting aquarium capacity to US gallons
Multiply the aquarium capacity in liters by 0.2641720524. For example, a nominal 100-liter aquarium equals approximately 26.4172 US gallons.
This conversion helps when comparing aquarium sizes, filters, heaters, lights, circulation pumps, water conditioners, medication instructions, and maintenance recommendations that use different volume units.
A tank's stated capacity is often a nominal or external volume. The actual amount of water inside the aquarium may be lower after substrate, rocks, decorations, equipment, air space, and incomplete filling are considered.
Enter the aquarium's liter capacity to calculate its nominal US-gallon equivalent.
Tank-volume calculation
Aquarium liters-to-US-gallons formula
Use the full liter capacity listed for the tank.
Both methods produce the same US-liquid-gallon result.
For an 80-liter tank:
An 80-liter aquarium is approximately 21.1338 US gallons nominally.
Manual method
How to convert an aquarium size step by step
Use a 120-liter aquarium as an example.
- 01
Find the stated liter capacity
Use 120 liters as the nominal tank volume.
- 02
Multiply by 0.2641720524
Calculate 120 × 0.2641720524.
- 03
Read the gallon result
The result is approximately 31.700646288 US gallons.
- 04
Distinguish nominal and actual volume
Report the tank as approximately 31.70 US gallons nominally, while recognizing that actual water volume may be lower.
Tank-size reference
Aquarium liters-to-US-gallons chart
| Nominal liters | US gallons | Rounded size |
|---|---|---|
| 10 L | 2.64172 US gal | 2.64 gal |
| 20 L | 5.28344 US gal | 5.28 gal |
| 30 L | 7.92516 US gal | 7.93 gal |
| 40 L | 10.56688 US gal | 10.57 gal |
| 50 L | 13.20860 US gal | 13.21 gal |
| 60 L | 15.85032 US gal | 15.85 gal |
| 75 L | 19.81290 US gal | 19.81 gal |
| 80 L | 21.13376 US gal | 21.13 gal |
| 100 L | 26.41721 US gal | 26.42 gal |
| 120 L | 31.70065 US gal | 31.70 gal |
| 150 L | 39.62581 US gal | 39.63 gal |
| 180 L | 47.55100 US gal | 47.55 gal |
| 200 L | 52.83441 US gal | 52.83 gal |
| 250 L | 66.04301 US gal | 66.04 gal |
| 300 L | 79.25162 US gal | 79.25 gal |
| 400 L | 105.66882 US gal | 105.67 gal |
| 500 L | 132.08603 US gal | 132.09 gal |
Worked tank conversions
Aquarium conversion examples
Convert a 54-liter aquarium
A 54-liter tank is approximately 14.27 US gallons nominally.
Convert a 90-liter aquarium
A 90-liter aquarium is approximately 23.78 US gallons nominally.
Convert a 180-liter aquarium
A 180-liter aquarium is approximately 47.55 US gallons nominally.
Usable water capacity
Why actual aquarium water volume is lower
The nominal volume may describe the tank's full geometric capacity. An operating aquarium rarely holds that amount of water.
- Substrate occupies part of the tank's internal volume.
- Rocks, wood, plants, and decorations displace water.
- Filters, heaters, and internal equipment occupy space.
- The water line usually remains below the top edge.
- Internal glass dimensions are smaller than external measurements.
- Sumps and external filters may add water volume to the complete system.
Use nominal size for broad product comparison. Use an estimate of actual system water volume when dosing or calculating water changes.
Rectangular tank calculation
Estimating aquarium liters from dimensions
For a rectangular tank measured internally in centimeters, multiply length, width, and water depth, then divide by 1,000.
Use internal measurements and actual water depth for a more practical estimate.
A tank with internal water dimensions of 80 cm by 35 cm by 40 cm contains approximately 112 liters before accounting for displaced water.
This equals approximately 29.59 US gallons before displacement.
Bow-front, cylindrical, corner, irregular, and tapered aquariums require shape-specific calculations.
Filter and heater comparison
Using converted volume for aquarium equipment
Filters, heaters, pumps, circulation equipment, and lighting may list recommended tank sizes in liters or US gallons.
Do not select equipment from volume alone. Stocking level, animal type, water temperature, room temperature, tank shape, flow requirements, and manufacturer instructions can affect suitability.
Nominal comparison
Do not use volume alone
Follow manufacturer guidance
Dosing and maintenance
Using liters and gallons for aquarium treatments
Water conditioners, medications, mineral products, salt, and other treatments may give instructions per liter or per US gallon.
Use the product's stated unit and follow its instructions. When converting, use actual system water volume rather than nominal tank capacity where possible.
Verify the product, concentration, species suitability, treatment purpose, and manufacturer instructions before adding anything to an aquarium.
Regional tank labels
US gallons and imperial gallons for aquariums
Aquarium sizes may be described using US gallons or imperial gallons depending on the market.
Used in this guide
Larger gallon unit
About 21.997 imperial gal
Accuracy check
Common aquarium conversion mistakes
Treating nominal capacity as actual water volume
Substrate, decorations, equipment, and air space reduce the amount of water inside the tank.
Mixing US and imperial gallons
Confirm the gallon standard used by the equipment or treatment instructions.
Using external tank dimensions
Glass thickness and frame dimensions can make external measurements larger than the internal water space.
Rounding too early
Keep the full liter value through the conversion and round only the final result.
Continue reading
Related liters-to-US-gallons guides
Questions and answers
Frequently asked questions
How many US gallons is a 100-liter aquarium?
One hundred liters equals approximately 26.4172 US gallons.
How many US gallons is a 200-liter aquarium?
Two hundred liters equals approximately 52.8344 US gallons.
Does a 100-liter tank hold exactly 100 liters of water?
Not necessarily. Substrate, decorations, equipment, air space, and tank construction can reduce actual water volume.
Should aquarium products be dosed from nominal capacity?
Use actual system water volume when possible and follow the product manufacturer's instructions.
Convert a volume
Use the Liters to US Gallons Converter
Enter any positive whole or decimal liter measurement to calculate US liquid gallons instantly.
Open Liters to US Gallons ConverterLast updated: July 27, 2026