How much substrate do I need for my tank?

Multiply your tank's base length by its width by the depth you want, then convert to weight. As a rough guide, a 5 cm bed needs about 1.5 kg of gravel per litre of bed volume. Enter your dimensions above for an exact figure for gravel, sand, or aquasoil.

How deep should my substrate be?

2.5–5 cm (1–2 inches) suits most tanks. Go to 5–7.5 cm for planted tanks that need rooting depth, and keep sand on the shallower side to avoid trapped gas pockets. Deeper isn't always better — it just adds weight and cost.

Does substrate reduce my water volume?

Yes. The bed fills the bottom of the tank, so it displaces water roughly equal to its own volume. A 5 cm bed in a 75-litre tank takes up around 11 litres, leaving about 64 litres of water — which is the number you should dose and stock against.

How much does aquarium gravel weigh?

Aquarium gravel has a bulk density of roughly 1.5 kg per litre, sand a little more at about 1.6 kg/L, and aquasoil much less at around 0.8 kg/L because it's porous and baked. The calculator uses these to turn your bed volume into a buy weight.

Add about 10% to the estimate. You'll lose a little when rinsing, want some to slope or top up as it settles, and bag weights are nominal. It's better to have a small surplus than to run short mid-setup.

Free aquarium calculator

Aquarium Substrate Calculator

Work out how much gravel, sand, or aquasoil you need. Enter your tank's base footprint and the bed depth, pick a substrate, and get the weight to buy plus how much water it displaces.

Base length

Base width

Bed depth

Most tanks use 2.5–5 cm (1–2 in); deeper, planted aquasoil beds run 5–7.5 cm (2–3 in).

cm / in

Substrate type

Substrate needed

Weight to buy

—

Bag volume — Water displaced —

Subtract this from your tank's rated volume to get the net water volume.

Results are estimates. Bulk density varies by brand and grain size — gravel and sand run heavy, aquasoil is light. Buy about 10% extra for slopes and to top up settling.

How the substrate calculator works

Enter the length and width of your tank's base and the depth of substrate you want, then choose gravel, sand, or aquasoil. The calculator multiplies the footprint by the depth to get the bed volume, converts that to a weight using the material's bulk density, and tells you how much water the bed displaces so you can adjust your net volume.

The formula

Bed volume is simply base length × base width × depth. We compute it in cubic centimetres and divide by 1,000 for litres, then multiply by bulk density: gravel ≈ 1.5 kg/L, sand ≈ 1.6 kg/L, and aquasoil ≈ 0.8 kg/L. Because the bed fills the bottom of the tank, the water it displaces equals that same bed volume.

Worked example

A 75 × 30 cm tank with a 5 cm gravel bed needs 75 × 30 × 5 = 11,250 cm³ = 11.25 litres of gravel, weighing about 17 kg. That same bed displaces roughly 11 litres of water, so a tank rated at 75 litres actually holds closer to 64 litres once the substrate is in.

How deep should the substrate be?

For most tanks 2.5–5 cm (1–2 inches) is plenty and keeps detritus from trapping. Planted tanks using aquasoil or wanting to root heavy stem plants often go 5–7.5 cm (2–3 inches), sometimes sloped deeper at the back for a sense of depth. Sand is usually kept shallower than gravel to avoid anaerobic pockets.

How much substrate for common tank sizes

Weight to buy for a 5 cm (2 in) bed, the most common depth, worked out with the calculator above. For a 2.5 cm (1 in) sand bed, halve the numbers; for a 7.5 cm (3 in) planted bed, multiply them by 1.5. Enter your own base size and depth above for an exact figure.

How much substrate for common tank sizes
Tank	Base (L × W)	Bed volume	Sand	Gravel	Aquasoil
10 gal	20 × 10 in · 51 × 25 cm	6.5 L	10.3 kg / 23 lb	9.7 kg / 21 lb	5.2 kg / 11 lb
20 long	30 × 12 in · 76 × 30 cm	11.6 L	18.6 kg / 41 lb	17.4 kg / 38 lb	9.3 kg / 20 lb
29 gal	30 × 12 in · 76 × 30 cm	11.6 L	18.6 kg / 41 lb	17.4 kg / 38 lb	9.3 kg / 20 lb
40 breeder	36 × 18 in · 91 × 46 cm	20.9 L	33.4 kg / 74 lb	31.4 kg / 69 lb	16.7 kg / 37 lb
55 gal	48 × 13 in · 122 × 33 cm	20.1 L	32.2 kg / 71 lb	30.2 kg / 67 lb	16.1 kg / 36 lb
75 gal	48 × 18 in · 122 × 46 cm	27.9 L	44.6 kg / 98 lb	41.8 kg / 92 lb	22.3 kg / 49 lb
125 gal	72 × 18 in · 183 × 46 cm	41.8 L	66.9 kg / 147 lb	62.7 kg / 138 lb	33.4 kg / 74 lb
40 L	20 × 10 in · 50 × 25 cm	6.3 L	10.0 kg / 22 lb	9.4 kg / 21 lb	5.0 kg / 11 lb
63 L	24 × 12 in · 60 × 30 cm	9.0 L	14.4 kg / 32 lb	13.5 kg / 30 lb	7.2 kg / 16 lb
101 L	31 × 14 in · 80 × 35 cm	14.0 L	22.4 kg / 49 lb	21.0 kg / 46 lb	11.2 kg / 25 lb
200 L	39 × 16 in · 100 × 40 cm	20.0 L	32.0 kg / 71 lb	30.0 kg / 66 lb	16.0 kg / 35 lb
300 L	47 × 20 in · 120 × 50 cm	30.0 L	48.0 kg / 106 lb	45.0 kg / 99 lb	24.0 kg / 53 lb
450 L	59 × 20 in · 150 × 50 cm	37.5 L	60.0 kg / 132 lb	56.3 kg / 124 lb	30.0 kg / 66 lb

Frequently asked questions

How much substrate do I need for my tank?: Multiply your tank's base length by its width by the depth you want, then convert to weight. As a rough guide, a 5 cm bed needs about 1.5 kg of gravel per litre of bed volume. Enter your dimensions above for an exact figure for gravel, sand, or aquasoil.
How deep should my substrate be?: 2.5–5 cm (1–2 inches) suits most tanks. Go to 5–7.5 cm for planted tanks that need rooting depth, and keep sand on the shallower side to avoid trapped gas pockets. Deeper isn't always better — it just adds weight and cost.
Does substrate reduce my water volume?: Yes. The bed fills the bottom of the tank, so it displaces water roughly equal to its own volume. A 5 cm bed in a 75-litre tank takes up around 11 litres, leaving about 64 litres of water — which is the number you should dose and stock against.
How much does aquarium gravel weigh?: Aquarium gravel has a bulk density of roughly 1.5 kg per litre, sand a little more at about 1.6 kg/L, and aquasoil much less at around 0.8 kg/L because it's porous and baked. The calculator uses these to turn your bed volume into a buy weight.
Should I buy extra?: Add about 10% to the estimate. You'll lose a little when rinsing, want some to slope or top up as it settles, and bag weights are nominal. It's better to have a small surplus than to run short mid-setup.