Aquarium Substrate Calculator
How much sand, gravel or soil your tank needs
Enter your tank size and the substrate depth you want, and get the exact amount to buy in pounds, kilograms and litres — plus a bag count rounded up, a side-by-side sand, gravel and aquasoil comparison, and the water your bed will displace.
Updated July 2026 · Reviewed by the AquariumStocking team
Tank & substrate depth
Substrate is calculated from the tank footprint, so bow-front, cylinder, hexagon and corner tanks come out right — not just length × width.
Shallower at the front, deeper at the back — we average the two.
1–2 in for fish-only, 2–3 in for planted.
Standard 2–5 mm aquarium gravel. Rinse thoroughly before use.
Typical gravel/sand bag.
Typical aquasoil bag.
Live 3D preview
Drag to rotate. The bed at the bottom is your substrate layer.
How much substrate you need
Rectangular tank · Gravel · 2.00 in average depth
This bed displaces roughly 2.0 US gallons (7.7 L), so your real water volume is lower than the tank's rated size. Use the net figure with the fish tank volume calculator and the dosing calculator.
Densities are estimates. Real weight varies with product, grain size and how damp the bag is — always round bag counts up so you don't run short mid-scape.
The formula
Your footprint is 360 in² (2323 cm²), giving 11.8 L of substrate at 1.5 g/cm³.
1 ft³ = 1728 in³ · 1 in = 2.54 cm · 1 kg = 2.205 lb.
Sand, gravel and aquasoil compared
The same tank and the same depth, but very different weights — aquasoil is roughly half the weight of sand for the identical bed. Pounds per gallon is shown against the tank footprint so you can sanity-check the usual rule of thumb.
| Substrate | Density | Pounds | Kilograms | 20 lb bags |
|---|---|---|---|---|
| Gravel | 1.5 g/cm³ · 95 lb/ft³ | 39.0 lb | 17.7 kg | 2 |
| Sand | 1.6 g/cm³ · 100 lb/ft³ | 41.6 lb | 18.9 kg | 3 |
| Aquasoil / planted substrate | 0.8 g/cm³ · 50 lb/ft³ | 20.8 lb | 9.4 kg | 2 |
| Crushed coral / aragonite | 1.4 g/cm³ · 90 lb/ft³ | 36.4 lb | 16.5 kg | 2 |
How deep should aquarium substrate be?
Substrate depth is a balance between what your plants and bottom dwellers need and what stays biologically safe. Shallow beds are easy to vacuum and never go sour; deep beds anchor roots but trap waste. Most tanks land between 1 and 3 inches (2.5–7.5 cm).
- Fish-only: 1–2 in (2.5–5 cm). Enough for looks and a bacterial bed, easy to keep clean.
- Planted: 2–3 in (5–7.5 cm) so stems and crypts can anchor properly.
- Carpets & heavy root feeders: about 3 in (7.5 cm), ideally a nutrient layer capped with sand or fine gravel.
- Sand for corydoras and loaches: keep it near 1–1.5 in so it can be stirred and never compacts hard.
Slopes read beautifully in aquascaping — shallower at the front, deeper at the back. Toggle the slope switch above and the calculator averages the two depths, which is the correct volume for a linear slope.
Don't go too deep
Past roughly 3–4 inches, oxygen stops reaching the lower layers and anaerobic pockets form. Those pockets can produce hydrogen sulfide — the rotten-egg smell released when a deep bed is disturbed — which is toxic to fish in an enclosed tank.
Only run beds deeper than 4 inches if they are densely planted with root-feeding species that oxygenate the substrate, or paired with an under-gravel setup. Otherwise poke the bed periodically with a chopstick and vacuum the top layer at water changes.
Frequently asked questions
Stock it for the bottom too
Substrate choice decides which bottom dwellers you can keep — corydoras, kuhli loaches and geophagus all need sand. Check your list before you buy gravel.
Net volume & planted maths
The volume calculator has a substrate-depth field too, so it subtracts this bed automatically. Then dial in ferts and CO₂ against that net figure.