Aquarium Volume Calculator
Calculate aquarium volume in litres and gallons for rectangular, bowfront, cylinder, hex and corner tanks.
Fill in the measurements โ the volume updates as you type.
- Total volume (to the brim)
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- US gallons
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- Imperial gallons
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- Actual water volume
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- Actual water (US gallons)
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- Water weight
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Volumes are geometric: they assume flat glass and ignore the displacement of rocks, wood, decor and equipment. A stocked tank typically holds 5โ10 % less water than the number above. Check the weight before choosing a stand โ a filled tank is heavy.
How it works
Every tank here is a prism or a cylinder, so the volume is simply the cross-sectional area of
the footprint multiplied by the water height. A rectangular tank is
V = L ร W ร H; a cylinder is V = ฯ ร rยฒ ร H; a half-cylinder and a
corner (quarter-cylinder) tank are the same figure halved and quartered; a regular hexagon
uses A = (3โ3 โ 2) ร sยฒ with s the side length; and a bowfront adds a
half-ellipse to the rectangle, A = L ร W + (ฯ โ 2) ร (L โ 2) ร bow. The result is
converted with the exact factors 1 US gallon = 3.785411784 L,
1 imperial gallon = 4.54609 L and 1 inch = 2.54 cm.
Substrate depth and the gap you leave below the rim are subtracted from the height, so the โactual water volumeโ is what you really need to dose, condition and heat โ usually the number you should use for fertiliser, medication and water-change maths. Water weight is 1 kg per litre for freshwater and 1.025 kg per litre for marine salt water, and does not include the glass, substrate or stand. Everything is calculated in your browser with plain JavaScript: no uploads, no accounts, no ads.
Frequently asked questions
How do I calculate my aquarium's volume in gallons?
Multiply the footprint area by the water height, then convert. For a rectangular tank that is length x width x height; a 120 x 40 x 50 cm tank is 240,000 cm3 = 240 litres = 63.40 US gallons (1 US gallon = 3.785411784 L) or 52.79 imperial gallons. In inches, divide cubic inches by 231 to get US gallons.
Why is my tank's real water volume less than the calculated volume?
The geometric volume assumes the tank is filled to the brim and empty inside. Substrate, the few centimetres you leave below the rim, rocks, wood and equipment all displace water. Enter your substrate depth and rim gap here and use the 'actual water volume' figure for dosing and water changes - a stocked tank typically holds another 5-10% less.
How much does a filled aquarium weigh?
Freshwater weighs 1 kg per litre (8.34 lb per US gallon) and saltwater about 1.025 kg per litre. A 240-litre freshwater tank therefore holds roughly 240 kg (529 lb) of water alone, before you add the glass, substrate, rock and stand - check the load rating of your furniture and floor.