Aquarium volume calculator for litres and gallons
This aquarium volume calculator tells you how much water your tank really holds. Pick a rectangle, cylinder, bow-front, hexagon, triangular corner or quarter-round corner tank, enter the dimensions in centimetres, millimetres, metres, inches or feet, and read the answer in litres, US gallons and UK gallons. Many online charts quote the “nominal” size of a tank; this tool works from your own measurements.
It also removes the things that take water’s place: the glass on the walls and base, the gap between the water line and the rim, the gravel or sand on the floor, and any rock or wood. The result is the net water volume you need for dosing, water changes, heater sizing and the weight your stand has to carry.
How to use the Aquarium Volume Calculator
- Choose the tank shape and the length unit. Tick whether your numbers were measured outside or inside the glass.
- Enter the dimensions shown in the boxes and the tank height. For a bow-front tank, the bow is how far the curved front sticks out past the straight sides.
- For outside measurements, enter the glass thickness (a typical small tank uses 4–6 mm; larger tanks use more).
- Set how far the water sits below the rim, the substrate depth and its pore space, and the volume of any rocks or wood.
- Read the net water in litres and gallons, then copy the result.
Aquarium Volume Calculator features
Six tank shapes
Rectangle, cylinder, bow-front, hexagon, triangular corner and quarter-round corner, each with its own geometry.
Glass deducted properly
Thickness comes off every wall and the base, so a 100 × 40 × 50 cm tank with 10 mm glass holds 182.5 L, not 200 L.
Substrate and decor
Gravel only displaces its solid part; the pores fill with water, so pore space is a setting.
Litres, US and UK gallons
A US gallon is 3.785 L and a UK gallon is 4.546 L, so the same tank is a different number of gallons on either side of the Atlantic.
Weight of the water
Fresh water is about 1 kg per litre, which is the load before glass, stand, substrate and equipment.
Formulas for each tank shape
Every shape here is a vertical prism, so volume is the floor area times the water depth. To convert, 1,000 cm³ is one litre, one US gallon is 231 cubic inches (3.785 L) and one UK gallon is 4.546 L. For other volume units or shapes, use the volume calculator or the volume converter.
| Shape | Footprint area | Volume |
|---|---|---|
| Rectangle | length × width | area × height |
| Cylinder | π × d² ÷ 4 | area × height |
| Hexagon (side s) | 3√3 ÷ 2 × s² | area × height |
| Triangular corner (legs a, b) | a × b ÷ 2 | area × height |
| Quarter-round corner (radius r) | π × r² ÷ 4 | area × height |
| Bow-front | rectangle + circular segment | area × height |
Worked example: a 60 × 30 × 36 cm tank
Outside, the tank is 60 × 30 × 36 cm = 64.8 L, the “nominal” volume. With 5 mm glass the inside is 59 × 29 cm and 35.5 cm tall, which is 60.7 L to the rim. Fill it to 2 cm below the rim and the water is 33.5 cm deep, about 57.3 L. Add 4 cm of gravel with 40 % pore space: its 6.8 L of bulk holds 4.1 L of solid, which pushes that much water aside and leaves about 53.2 L. That figure, not 64.8 L, is the one to use for dosing.
Things the calculator cannot know
- Glass strength. The tool subtracts the thickness you enter but does not say whether it is thick enough. Glass or acrylic thickness depends on height, bracing and the maker’s safety factor, so follow the manufacturer’s specification.
- Rounded corners and seams. Silicone beads, bracing and rounded edges remove a little more volume than the model does.
- Bow-front inside shape. The inside curve is approximated by shifting the arc inward by the glass thickness; the error is small for thin glass.
- Fish and plants. This is geometry only. For how many fish a tank suits, see the fish tank stocking calculator and ask an aquarium specialist or vet about your species.
Aquarium Volume Calculator FAQ
How do I calculate the volume of an aquarium in litres?
Multiply length × width × height in centimetres and divide by 1,000. A 60 × 30 × 36 cm tank is 64,800 cm³, or 64.8 litres, before glass, substrate and the gap under the rim.
How many gallons is my fish tank?
Divide litres by 3.785 for US gallons or by 4.546 for UK gallons. A 100-litre tank is 26.4 US gallons or 22.0 UK gallons.
Do I measure inside or outside the glass?
Either. Outside is easier with a tape measure, so enter the glass thickness and the calculator subtracts it. If you measured inside the tank, choose “Inside” and no glass is removed.
How do I find the volume of a bow-front tank?
Treat it as a rectangle plus a curved segment. Enter the length, the total depth at the bulge and how far the front bulges, and the tool adds the circular segment to the rectangle.
How much does the water in an aquarium weigh?
Fresh water is about 1 kg per litre (8.3 lb per US gallon). A 200-litre tank holds 200 kg of water, plus glass, stand, substrate and equipment.
Does gravel change the water volume?
Yes. Gravel and sand occupy space, although water fills the gaps between grains. The calculator takes off only the solid share, using the pore space you set (30–45 % is typical).