Free Online Calculators
Calculate volume, heater & filter power
The aquarium calculator works out your tank's exact water volume from its length, width, and height, then recommends the right heater wattage and filter flow rate. Volume is calculated as length × width × height (in cm) ÷ 1000 to get litres. It takes the guesswork out of choosing equipment for a healthy, balanced tank.
Thanks for your feedback!
Multiply length by width by height in inches to get cubic inches, then divide by 231, the number of cubic inches in one US gallon. Measure the inside dimensions and use the actual water height if you want the filled volume. The calculator on this page works in centimeters and liters: enter the outer dimensions in cm (inches × 2.54) and divide the liters by 3.785 for US gallons.
24 × 16 × 12 inches is 4,608 cubic inches; divided by 231 that is about 19.9 US gallons (about 75 liters), brim-full and measured on the outside. The real water volume is lower once the glass, substrate, rocks and the gap below the rim are counted. The calculator here takes centimeters, so enter 61 × 40.6 × 30.5 cm to see the net liters.
36 × 17 × 18 inches is 11,016 cubic inches, which is about 47.7 US gallons or 180 liters brim-full. Subtract a little for the glass, substrate and the unfilled top edge. To use the calculator here, enter the dimensions in centimeters (inches × 2.54); it shows liters.
There is no reliable fixed formula. Look at the adult size of each species, its swimming and schooling behavior, how much waste it produces and the minimum tank size it needs, then check that filtration and water changes can keep up. The calculator on this page does not give a stocking figure; it shows volume, heater wattage and filter flow.
No, a one gallon tank is far too small for three guppies. Guppies are active, breed quickly and produce enough waste that ammonia spikes fast in such a small volume, so a properly filtered and cycled tank of several gallons is the minimum.
24 × 12 × 12 inches is 3,456 cubic inches, or about 15 US gallons (roughly 57 liters). That is the full-to-the-rim capacity measured on the outside, so plan on somewhat less actual water. The calculator here works in centimeters and liters.
30 × 12 × 12 inches is 4,320 cubic inches, about 18.7 US gallons or 71 liters. Substrate, decor, the glass and the gap under the rim reduce the real water volume. For the calculator on this page, enter the dimensions in centimeters (inches × 2.54).
24 × 24 × 24 inches is 13,824 cubic inches, about 59.8 US gallons or 226 liters brim-full. A cube tank has less surface area per gallon than a long tank of the same volume, which matters for gas exchange and stocking.
20 × 10 × 12 inches is 2,400 cubic inches, about 10.4 US gallons or 39 liters. Fill height rather than full tank height gives you the true water volume. The calculator here takes centimeters, so enter 50.8 × 25.4 × 30.5 cm to see the liters.
How much water does your tank hold, how heavy is it when full and what equipment suits it? The aquarium calculator takes the outer dimensions and the glass thickness and returns the net and gross volume, the water weight and guide values for heater wattage and filter flow.
Substrate, rocks, decorations and the gap between the water surface and the rim reduce the real amount of water further. The calculator does not subtract them. If the water line sits 3 cm below the rim, an 80 × 35 cm tank with 6 mm glass holds about 8 liters less.
All inputs are in centimeters and the results are in liters. For a tank measured in inches, multiply each dimension by 2.54 first; one US gallon is 3.785 liters.
The gross volume is 80 × 35 × 45 ÷ 1,000 = 126 liters. The net volume is (80 − 1.2) × (35 − 1.2) × (45 − 0.6) ÷ 1,000 ≈ 118 liters, so about 118 kg of water. The calculator suggests about 118 watts of heating and a filter flow of about 355 liters per hour.
The suggestion follows the rule of thumb of 1 watt per liter. The calculator does not ask for room or water temperature and does not adjust the value. If the tank stands in a cool room or the water should be much warmer than the room, choose a stronger heater.
The calculator uses a turnover of three times the net volume per hour. Many fishkeepers choose a higher turnover for heavily stocked tanks; compare the figure with the hourly flow of the filter you plan to buy.
The calculator gives no stocking recommendation. How many fish a tank can hold depends on the species, adult size, behavior, layout and filtration. Read up on the species you want to keep.
Length × width × height in centimeters, divided by 1,000, gives liters. The calculator also subtracts the glass thickness and shows the net volume; it does not subtract substrate or decorations.
Outer dimensions. The calculator subtracts the glass itself. If you enter inner dimensions, the glass is subtracted twice. If you only have inner dimensions, calculate length × width × water height ÷ 1,000 directly.
The calculator uses 1 watt per liter of net volume, so about 118 watts for 118 liters. Temperatures are not part of the calculation.
The calculator suggests three times the net volume per hour, so 300 liters per hour for a tank with 100 liters net.
Yes, it is free and needs no registration.