Convert Aquarium Gallons to Liters

Direct answer

Multiply aquarium capacity in US gallons by 3.785411784.

For example, a 20-gallon aquarium converts to:

Rounded to two decimal places, this is 75.71 liters.

Use the US Gallons to Liters Converter for another aquarium size.

Common aquarium sizes in liters

Example: convert a 10-gallon aquarium

Example: convert a 29-gallon aquarium

Rounded to two decimal places, this is 109.78 liters.

Example: convert a 55-gallon aquarium

Rounded to two decimal places, the nominal capacity is 208.20 liters.

Nominal aquarium capacity versus actual water volume

A tank sold as a 20-gallon aquarium may not hold exactly 20 gallons of water during normal use.

Actual water volume can be reduced by:

• substrate;
• rocks and decorations;
• wood and plants;
• internal filters;
• equipment displacement;
• space below the rim;
• tank-wall thickness;
• manufacturer rounding.

The gallon-to-liter conversion accurately converts the stated capacity, but it does not measure the current water volume.

Calculating water-change volume

A water-change percentage should ideally use the actual working water volume rather than only the marketed tank size.

Example using a nominal 20-gallon tank

If decorations and equipment reduce actual water volume to 65 liters, then a 25 percent water change would be 16.25 liters instead.

Filter flow ratings

Filters and pumps may be rated in gallons per hour or liters per hour. Tank-capacity conversion changes only the aquarium volume. Flow-rate conversion also includes the time unit.

Keep these measurements separate:

• tank capacity in gallons or liters;
• filter flow in gallons per hour;
• filter flow in liters per hour;
• turnover rate per hour.

Heaters, treatments, and aquarium products

Aquarium products may provide instructions based on liters or gallons. Confirm whether the instructions refer to actual water volume, nominal tank capacity, or a recommended equipment range.

A unit conversion does not determine:

• appropriate stocking;
• heater wattage;
• medication dosage;
• water-treatment quantity;
• filter suitability;
• species-specific care.

Follow the relevant product instructions and qualified care guidance.

US gallons versus Imperial gallons for aquariums

Aquarium sizes from different markets may use different gallon definitions.

The difference is substantial, so confirm whether the tank is described using US or Imperial gallons.

Estimating aquarium liters mentally

Multiply US gallons by 4 for a quick estimate.

This estimate is useful for a quick comparison but should not be used for precise product dosing or equipment calculations.

Common aquarium conversion mistakes

Assuming marketed capacity equals actual water volume

Substrate, decorations, equipment, and headspace reduce the amount of water present.

Using Imperial gallons instead of US gallons

Check the tank's market and manufacturer specifications.

Confusing capacity with flow rate

Gallons and liters measure volume, while gallons per hour and liters per hour measure flow.

Using nominal volume for precise dosing without checking

Product instructions may require actual water volume.

Rounding the aquarium size before conversion

Convert decimal or unusual sizes directly.

Related US gallons to liters guides

Frequently asked questions