🐠 Aquarium Volume Calculator
Enter your tank's length, width and height to get its volume in litres and gallons, plus the real water volume after substrate and the rim.
Volume
200 L
US / UK gallons
52.8 / 44
Approx. water (−10%)
180 L
Volume = length × width × height. Use the inside dimensions; actual water volume is roughly 10% less once substrate, rocks and the gap below the rim are accounted for. 1 L = 0.264 US gallons. 🔒 In your browser.
How the aquarium volume calculator works
A rectangular tank's volume is length × width × height. The tool computes it from centimetres or inches, converts to litres and both US and UK gallons, and also shows an approximate real water volume — about 10% less — because substrate, rocks, decorations and the gap below the rim all displace water.
Knowing the true volume matters for dosing medications and water treatments, calculating filter turnover, and stocking. Use the inside dimensions, and remember that a "20-gallon" marketed tank rarely holds exactly 20 gallons of water once it's set up.
Frequently asked questions
How do I calculate aquarium volume?
Multiply length × width × height (inside dimensions). In centimetres, divide by 1,000 for litres: a 100 × 40 × 50 cm tank is 200,000 cm³ = 200 litres (about 53 US gallons).
How many gallons is my fish tank?
Work out the volume in litres, then divide by 3.785 for US gallons or 4.546 for UK gallons. The tool shows both. A 200-litre tank is about 53 US or 44 UK gallons.
Why is the actual water volume less than the tank size?
Substrate, rocks, décor and the few centimetres of air below the rim all take up space, so the real water volume is typically around 10% less than the raw dimensions suggest. The tool shows this adjusted figure.
Why does tank volume matter for dosing?
Medications, dechlorinator and fertilisers are dosed per unit of water. Using the true water volume (not the marketed tank size) avoids under- or over-dosing, which can harm fish or fail to treat them.
Does the calculator work for US and UK gallons?
Yes — it shows both, because a US gallon (3.785 L) and a UK gallon (4.546 L) differ by about 20%. Make sure you know which your equipment or medication assumes.