Aquarium substrate calculator

Enter your tank's floor measurements and the depth you want, level or sloped, and see how many litres of substrate that takes, roughly what it weighs and how many bags to buy.

How the amount is worked out

The calculator multiplies the area of the tank floor by the depth of the bed. The floor area uses the same shape maths as our aquarium volume calculator, so rectangular, round, bow-front, corner and hexagonal tanks all work.

A sloped bed, deeper at the back than at the front, holds the same as a level bed at the average of the two depths. A 90 × 45 cm tank sloped from 3 cm at the front to 9 cm at the back needs 24.3 litres, exactly the same as a level 6 cm bed.

How deep should the substrate be?

There is no single right depth. It depends on what the bed has to do. As a starting point:

Planted tanks: most aquasoil layouts use around 5 to 8 cm, often sloped deeper towards the back, where the larger plants and their roots go.
Unplanted freshwater: 3 to 5 cm of sand or gravel is enough to cover the base and anchor decor.
Reef tanks: many keepers run a shallow sand bed of 2.5 to 5 cm, and some leave the bottom bare.
Burrowing fish: jawfish, and some gobies and wrasses, dig into the sand or sleep buried in it, so they need a deeper bed. Check the needs of the species you plan to keep.

Bottom-sifting fish such as corydoras forage through the substrate with their barbels, so they do best on fine, smooth sand rather than sharp gravel.

Litres, weight and bags

The litres are exact for the measurements you give. The weight is an estimate, because it depends on grain size, how tightly the product packs and how damp it is. The calculator uses typical loose, dry densities from standard engineering tables: about 1.44 kg per litre for sand, 1.28 for gravel and 1.52 for aragonite, which is close to crushed limestone. For aquasoil it uses about 0.9 kg per litre, the weight of damp soil as it comes in the bag.

Aquasoils such as ADA Amazonia are sold by volume, so buy those by the litre and ignore the weight. Sand and gravel are usually sold by weight: enter the bag size and the calculator rounds up to whole bags. If a packet states both litres and kilograms, the litres are the better figure to buy by.

Before you buy

Round up. The calculator already rounds to whole bags, and a little spare lets you adjust the slope as you aquascape.
Rinse sand and gravel before they go in, but not aquasoil: rinsing breaks down the granules.
Measure inside the glass. Outside measurements overstate the floor, by a few percent on a large tank with thick glass.
Substrate takes the place of water. Once you know your bed depth, the volume calculator can take it off your tank's water volume.

Common questions

How much sand do I need for my aquarium?

Multiply the length and depth of the tank floor by the depth of sand you want. Working in centimetres, divide by 1,000 for litres: a 60 × 30 cm tank with 5 cm of sand needs 9 litres, which is roughly 13 kg.

How many bags of substrate do I need?

Divide the amount you need by the bag size, in the same unit, and round up. Enter the bag size in litres or kilograms and the calculator does this for you.

How deep should aquasoil be for plants?

Around 5 to 8 cm suits most planted layouts, with the deeper part at the back for larger plants with big root systems. Carpeting plants at the front manage with less.

Why is the weight only approximate?

Two bags of sand with the same volume can differ in weight by 10% or more, depending on grain size and moisture. The volume is what fills the tank; the weight is a guide to what you will be carrying.

Does substrate reduce my tank's water volume?

Yes. The substrate bed takes the place of water across the whole floor, so a 5 cm bed in a 60 × 30 cm tank leaves room for 9 litres less water. The volume calculator can take your substrate depth into account.