How do I calculate the volume of my fish tank?

For a rectangular tank, multiply the length by width by height in centimetres, then divide by 1,000 to convert to litres. For example, a 60cm x 30cm x 35cm tank holds 63 litres. Remember to subtract the volume displaced by substrate, decorations, and equipment for a more accurate usable water volume.

How many fish can I keep in my tank?

A widely used guideline is roughly 1 cm of fish per litre of net water volume. So a 60-litre tank (after substrate) could house around 60 cm of total adult fish length. This is a starting point only. Some species need more space, and filtration capacity, plant coverage, and water parameters all affect stocking levels.

How heavy is a full fish tank?

Water weighs 1 kg per litre, so a 100-litre tank holds 100 kg of water alone. Add the weight of the tank glass, substrate, decorations, and stand. A filled 60-litre aquarium with gravel and glass typically weighs around 75 to 85 kg total. Always check that your furniture or stand can support the full weight.

Fish Tank Volume Calculator

Calculate aquarium volume in litres plus water weight

Published by UltraCalculatorsLast reviewed: 28 Mar 2026v1.0Report an issue

Knowing your fish tank's exact volume is essential for keeping healthy fish. Correct dosing of water treatments, filters, and heaters all depend on accurate volume measurements. Under- or over-estimating can lead to incorrect medication doses or inadequate filtration, both of which harm your fish. In the UK, aquarium volumes are typically measured in litres. Whether you have a standard rectangular tank, a cylindrical column tank, or a bow-front display aquarium, each shape requires a different formula. You also need to account for the volume displaced by substrate (gravel, sand, or soil) at the bottom of the tank. Our fish tank volume calculator handles all three common tank shapes, subtracts the substrate displacement, and gives you the net usable water volume in litres, the water weight in kilograms, and an approximate stocking guide based on the widely used centimetre-per-litre rule.

How to Use This Calculator

To calculate your fish tank volume: 1. Select your tank shape. Rectangular is the most common. Cylindrical suits column tanks. Bow-front adds roughly 15% extra volume compared to a rectangular tank of the same measurements. 2. Enter the tank length in centimetres (front to back for cylindrical tanks, this is the diameter). 3. Enter the tank width in centimetres (this is the side-to-side measurement; for cylindrical tanks this field is not used). 4. Enter the tank height in centimetres, measured from the bottom glass to the water line. 5. Enter the substrate depth in centimetres. The default 3 cm suits a thin layer of gravel. Set to 0 if your tank has no substrate. 6. Review results showing gross volume, net volume after substrate, water weight, and a fish stocking estimate.

How It Works

The volume formulas differ by tank shape: Rectangular: Volume (cm3) = Length x Width x Height Cylindrical: Volume (cm3) = Pi x (Diameter/2)^2 x Height Bow-front: Volume (cm3) = Length x Width x Height x 1.15 (roughly 15% more than rectangular) Converting to litres: Volume (litres) = Volume (cm3) / 1,000 Substrate displacement: Substrate Volume = Base Area x Substrate Depth / 1,000 Net Volume = Gross Volume - Substrate Volume Water Weight (kg) = Net Volume (litres) x 1 (water weighs 1 kg per litre) Fish estimate uses roughly 1 cm of adult fish per litre of net volume. For example, a 60cm x 30cm x 35cm rectangular tank: Gross = 63.0 litres. With 3 cm substrate: Substrate = 60 x 30 x 3 / 1,000 = 5.4 litres. Net = 57.6 litres, weight = 57.6 kg, fish estimate = approximately 57 cm of fish.

Worked Examples

Example 1: Standard rectangular aquarium

Inputs: Shape: Rectangular. Length: 60 cm. Width: 30 cm. Height: 35 cm. Substrate: 3 cm.

Gross volume = 60 x 30 x 35 = 63,000 cm3 = 63.0 litres.
Substrate volume = 60 x 30 x 3 = 5,400 cm3 = 5.4 litres.
Net volume = 63.0 - 5.4 = 57.6 litres.
Water weight = 57.6 kg.
Fish estimate = roughly 57 cm of adult fish.

Result: Gross volume is 63.0 litres, with a net usable volume of 57.6 litres after substrate. The water alone weighs 57.6 kg, so ensure your stand or furniture can support the total weight including tank and gravel.

Example 2: Large cylindrical column tank

Inputs: Shape: Cylindrical. Length (diameter): 40 cm. Width: not used. Height: 60 cm. Substrate: 5 cm.

Gross volume = Pi x (40/2)^2 x 60 = 3.1416 x 400 x 60 = 75,398 cm3 = 75.4 litres.
Substrate volume = Pi x (40/2)^2 x 5 = 6,283 cm3 = 6.3 litres.
Net volume = 75.4 - 6.3 = 69.1 litres.
Water weight = 69.1 kg.
Fish estimate = roughly 69 cm of adult fish.

Result: A 40 cm diameter, 60 cm tall cylinder holds 75.4 litres gross and 69.1 litres net. Column tanks have a smaller surface area for gas exchange, so consider stocking slightly below the maximum.

Example 3: Bow-front display tank

Inputs: Shape: Bow-front. Length: 80 cm. Width: 35 cm. Height: 45 cm. Substrate: 4 cm.

Base rectangular volume = 80 x 35 x 45 = 126,000 cm3.
Bow-front adjustment = 126,000 x 1.15 = 144,900 cm3 = 144.9 litres.
Substrate volume = 80 x 35 x 4 x 1.15 / 1,000 = 12.9 litres.
Net volume = 144.9 - 12.9 = 132.0 litres.
Water weight = 132.0 kg.

Result: The bow-front tank holds approximately 144.9 litres gross and 132.0 litres net. At over 130 kg of water weight, a dedicated aquarium stand is essential.

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