Substrate calculator
Work out exactly how much gravel, sand, or aqua soil to buy. Enter your tank's floor dimensions and how deep you want the bed, and this tells you the volume, the weight, and how many bags to pick up.
Updated 22 June 2026
Not sure what to use or how deep to go? Our substrate guide compares gravel, sand, and soil and covers depth by tank type. The floor dimensions are the same length and width you'd enter in the tank volume calculator.
Results
Substrate settles, and you'll usually slope it higher toward the back, so round up and keep a spare bag rather than running short mid-setup. Colours and grain rarely match exactly between batches.
How this calculator works
It multiplies your tank's floor area by the bed depth to get the volume, then turns that into a weight. Tank height isn't used, because substrate only covers the floor.
The weight allows about 1.5 kg per litre for gravel and sand. Aqua soil is lighter (roughly 0.5 to 0.8 kg per litre) and usually sold by the litre, so go by the volume figure for it. The bag count is the total divided by your bag size, rounded up.
How deep should it go?
For most community tanks, aim for 3 to 5 cm, a little deeper toward the back for a sense of depth. Keep sand beds shallower, around 3 to 4 cm, because a deep, undisturbed sand bed can trap pockets of gas. Heavily planted tanks and carpeting plants want more, up to 6 to 8 cm, to give roots room. Our substrate guide covers depth by tank type in more detail.
Why getting the amount right matters
Substrate is one of the hardest things to change once a tank is running and stocked, so it's worth getting the quantity right the first time. Running short halfway through a setup means matching a second batch to the first, and that's exactly when colours and grain size fail to line up.
From here: choose the right type in our substrate guide, and the same length and width you entered here will also give you your tank's water volume in the tank volume calculator (just add the height). If you're weighing up a chemistry-shifting substrate like crushed coral, the hardness converter helps you read the numbers. Keeping corydoras or other bottom-dwellers? They need smooth sand rather than sharp gravel, whatever the quantity.