Aquarium Volume Unit Converter

Convert any aquarium volume measurement between US gallons, liters, imperial gallons, cubic inches, cubic feet, and cubic centimeters. Enter a value in any field — all other units update instantly. Before entering a value, take accurate inside dimensions following how to measure aquarium volume.

Volume Unit Converter

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Aquarium Volume Conversion Reference

From To Exact Factor Example
US Gallons Liters × 3.785411784 55 gal = 208.2 L
US Gallons Imperial Gallons × 0.832674 55 gal = 45.8 imp gal
US Gallons Cubic Inches × 231 55 gal = 12,705 in³
US Gallons Cubic Feet × 0.133681 55 gal = 7.35 ft³
US Gallons Cubic Centimeters × 3,785.41 55 gal = 208,198 cm³
Liters US Gallons × 0.264172 200 L = 52.8 gal
Liters Imperial Gallons × 0.219969 200 L = 44.0 imp gal
Cubic Inches US Gallons ÷ 231 4,620 in³ = 20.0 gal
Cubic Feet US Gallons × 7.48052 1 ft³ = 7.48 gal
Imperial Gallons US Gallons × 1.20095 10 imp gal = 12.0 gal

The US gallon is legally defined as exactly 231 cubic inches. The imperial (UK) gallon equals 277.419 cubic inches — approximately 20% larger than the US gallon. For common tank volumes alongside their footprint dimensions, see aquarium volume by size.

Why Unit Conversion Matters for Aquarium Volume

Most aquarium products sold in North America use US gallons; products sold in Europe, Australia, and Asia use liters. Dosing instructions, filter ratings, and pump flow rates all reference volume units — using the wrong unit can result in a 20% dosing error (the difference between US and imperial gallons) or a 3.8× error (confusing liters with gallons).

Cubic inches appear in volume calculations because the US gallon is defined as exactly 231 cubic inches. When you multiply inside dimensions in inches, the result is cubic inches — dividing by 231 gives US gallons.

Cubic feet appear in aquarium contexts primarily for flow rate calculations. Filter and pump manufacturers sometimes rate flow in gallons per hour but calculate sump dimensions in cubic feet. A 1-cubic-foot sump holds 7.48 US gallons.

Imperial gallons (UK gallons) are 20% larger than US gallons. A product dosed at “1 ml per imperial gallon” requires 20% less product per US gallon. Always confirm which gallon standard a product label uses.

For a full metric-first reference including common tank sizes in centimetres and litres, see the aquarium volume in litres guide.

Because actual water volume is typically 10–15% below the nominal label after substrate, rocks, and the fill gap, dose against actual volume rather than the rated capacity — use the aquarium displacement calculator to refine your figure before converting units. To calculate volume for any tank shape, start with the free aquarium volume calculator.

Unit Conversion Questions

How many liters are in a US gallon?
One US gallon equals exactly 3.785411784 liters. This conversion factor is derived from the legal definition of the US gallon (231 cubic inches) and the metric definition of the liter (1,000 cubic centimeters). For quick estimates, use 3.785 liters per gallon.
What is the difference between a US gallon and an imperial gallon?
A US gallon equals 231 cubic inches (3.785 liters). An imperial (UK) gallon equals 277.419 cubic inches (4.546 liters) — about 20% larger. Most aquarium products sold in North America use US gallons. Always check which standard a product label references before dosing.
How do I convert cubic inches to gallons for my aquarium?
Divide the cubic inch volume by 231. For example, a tank with inside dimensions of 48 × 13 × 21 inches has a volume of 13,104 cubic inches. Divide by 231 to get 56.7 US gallons. The number 231 comes from the legal definition of the US gallon.
How do I convert aquarium liters to US gallons?
Multiply liters by 0.264172, or divide by 3.785411784. For example, 200 liters ÷ 3.785 = 52.8 US gallons. Most aquarium calculators outside the United States display results in liters; use this factor to convert to US gallons for North American product dosing.
Why do pump and filter ratings use gallons per hour instead of liters?
In North America, flow rate is conventionally expressed in gallons per hour (GPH) because the US gallon is the standard volume unit for aquarium equipment sold in that market. Internationally, flow rates are expressed in liters per hour (LPH). To convert GPH to LPH, multiply by 3.785. A pump rated at 300 GPH moves approximately 1,136 liters per hour.
What is a cubic foot in aquarium terms?
One cubic foot equals 1,728 cubic inches or 7.48052 US gallons. Cubic feet appear in aquarium contexts primarily when calculating sump dimensions, as sumps are sometimes built from lumber or acrylic sheet and measured in feet. A sump measuring 2 ft × 1 ft × 1 ft holds 2 cubic feet = 14.96 US gallons.

Related Tools and References

Aquarium Volume Formulas

See the complete formula reference for all 20 tank shapes
Aquarium Volume by Size

Standard tank sizes in gallons and liters
Aquarium Volume FAQ

Answers to common volume calculation questions
How to Measure Aquarium Volume

Step-by-step measurement guide for every shape
Aquarium Volume Glossary

Definitions of every term used in volume calculations
Rectangular Aquarium Volume Calculator

Calculate volume for standard rectangular tanks