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Aquarium volume calculator
Enter the dimensions of your tank to see how much water it really holds. Use this figure to dose fertiliser, medication and water changes.
How it is calculated
Gross volume = length × width × height ÷ 1000 (all in cm, result in litres). That is usually the figure on the box, but a tank never holds that much water.
For the net volume the calculator subtracts what is not water: the substrate layer (length × width × substrate depth), the strip between the water surface and the rim, and a share for rocks and wood. With outside dimensions it also subtracts the glass: twice the thickness for length and width, once for the height (bottom pane).
As a rule of thumb, a normally furnished tank ends up at 80 to 85 % of its gross volume. A 100 × 40 × 50 cm tank has 200 litres gross and a little over 160 litres of water.
Which volume for what?
- Fertiliser, water conditioner, medication: always the net volume. Dosing for the gross figure gives 15 to 20 % too much.
- Water changes: a percentage of the net volume, i.e. the litres you actually replace.
- Filter: manufacturers usually quote gross litres. A filter rated slightly above your tank does no harm.
- Stocking: litres alone say little. How many fish fit depends on the floor area, see the stocking calculator.
Enter it once, calculate correctly every time
In Aqualizer you enter your tank dimensions once. Water changes, CO₂, RO water and stocking then use your tank without measuring again.
- Dimensions and litres saved per tank
- Water changes with reminders
- Stocking density by floor area
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Aquarium volume FAQ
How do I calculate the volume of my aquarium?
Length × width × height in centimetres, divided by 1000, gives the litres. An 80 × 35 × 45 cm tank has 126 litres gross. After substrate, decor and the rim, a little over 100 litres of water remain.
How much water is really in the tank?
Usually 80 to 85 % of the gross volume. Substrate, rocks, wood and the gap between water and rim take up the rest. The calculator above subtracts each of them.
Inside or outside dimensions?
The calculation uses inside dimensions. If you only know the outside dimensions, tick “outside dimensions” and enter the glass thickness, usually 4 to 10 mm. The calculator then subtracts the glass.
How heavy is a filled aquarium?
Roughly 1.3 kg per litre of gross volume: water, glass, substrate and decor together. A 200-litre tank therefore weighs about 260 kg, plus the stand.
How much water do I change at 30 %?
30 % of the net volume. With 160 litres of water that is 48 litres. The calculator shows the amount for the chosen share directly.