Aquarium Volume Calculator
Calculate the exact volume of your tank in litres and gallons from its dimensions.
How it works
Rectangular: Volume (L) = Length × Width × Height (cm) ÷ 1000. Cylinder: V = π × r² × Height ÷ 1000. Subtract ~10% for substrate, rocks and the gap below the rim to estimate true water volume.
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Formula & Method
Rectangular: Volume (L) = Length × Width × Height (cm) ÷ 1000. Cylinder: V = π × r² × Height ÷ 1000. Subtract ~10% for substrate, rocks and the gap below the rim to estimate true water volume.
Example Calculation
A 60 × 30 × 36 cm tank = 60 × 30 × 36 ÷ 1000 = 64.8 L gross. After ~10% for substrate and rim gap, expect about 58 L of actual water.
Frequently Asked Questions
Why is my real water volume less than the calculated volume?
Substrate, rocks, driftwood and the gap between the water line and the rim all displace water. Subtract roughly 10-15% from the gross figure for a typical community tank, and up to 20-25% for a heavily aquascaped planted tank with deep substrate.
How do I convert litres to gallons?
Divide litres by 3.785 for US gallons, or by 4.546 for imperial (UK and older Australian) gallons. Most online fishkeeping advice is American, so assume US gallons unless the source says otherwise.
How many litres is a 4ft fish tank?
A standard Australian four-foot tank measuring 120 × 45 × 45 cm holds 243 litres gross, or roughly 214 litres of actual water once substrate and the rim gap are accounted for. Taller 120 × 45 × 60 cm tanks hold 324 litres gross.
How many litres is a 2ft fish tank?
A standard two-foot tank at 60 × 30 × 30 cm holds 54 litres gross and about 48 litres of water. The taller 60 × 30 × 38 cm version holds 68 litres gross, around 60 litres of water.
Should I measure the inside or the outside of the tank?
Always the inside. Glass is typically 8-10 mm thick on a four-foot tank, and using external dimensions overstates the volume by 3-5%.
How do I calculate the volume of a bow-front tank?
Calculate the rectangular section first, then add the bow as a segment of a cylinder. As a working approximation, a standard bow-front holds about 5-8% more than the equivalent rectangular tank of the same nominal dimensions.
Does the sump count towards total system volume?
Yes. For dosing and stocking purposes, use the combined water volume of the display tank plus the operating water level in the sump. A sump typically adds 20-30% to a marine system's total volume.
How much does substrate reduce water volume?
A 3 cm layer across a 120 × 45 cm footprint is about 16 litres of material, but roughly a third of that space holds water between the grains, so the net loss is around 11 litres. Deeper aquasoil layers in planted tanks displace considerably more.
What tank volume do I need for my fish?
It depends on adult size, activity level and whether the species shoals. Use our stocking calculator alongside the minimum tank litres stated on each species care guide, and treat those minimums as a floor rather than a target.