Substrate calculator: how many litres and kilograms to buy
Substrate is sold by weight but needed by volume — tank footprint × depth. Buy too little and you cannot finish the slope; buy too much and you are storing 10 kg of wet sand forever. This calculator converts your floor area and target depth into litres, then into the kilograms you will actually see on the bag, for the three common substrate families.
Key takeaways
- Volume is exact geometry: area × depth. The weight conversion uses bulk densities — approximations, clearly labelled.
- Common depth guidance: ~5–7.5 cm (2–3 in) planted, ≤5 cm (2 in) fish-only, bare bottom for some setups.
- Substrate displaces real water volume — subtract it before dosing anything.
The calculator
| Volume needed | — |
| Weight to buy | — |
| Weight (imperial) | — |
Sand: ~1.6 kg per litre of tank floor volume (bulk, incl. air gaps).
Methodology
The volume calculation is plain geometry: floor length × width × depth ÷ 1000 = litres, treating the bed as a uniform slab (if you slope front-to-back, use the average depth). Weight applies bulk densities — the mass of dry material that fills one litre of tank space, air gaps included. Commonly used hobby figures are ≈1.6 kg/L for sand, ≈1.5 kg for gravel and ≈0.8 kg for aquasoils, consistent with engineering bulk densities for sand and aggregate (roughly 1.4–1.7 kg/L depending on grading). Treat them as buying estimates, not lab values: manufacturers' grain mixes vary, and wet substrate weighs more.
Worked example: the default 60 × 30 cm floor at 5 cm of sand needs 60 × 30 × 5 ÷ 1000 = 9 L, which at 1.6 kg/L is about 14.4 kg (31.7 lb) — roughly one and a half standard 10 kg bags. The same footprint in aquasoil is only 7.2 kg, which is why planted-tank soil often looks cheap by the bag until you run the numbers per litre.
Sources
- AquariumCalc substrate calculator: 2–3 in planted depth guidance and kg/L figures used across hobby calculators (checked 2026-11-16).
- Aquarium Co-Op — substrate for planted aquariums: sand/gravel/soil trade-offs (checked 2026-11-16).
- Bulk density cross-check: standard engineering ranges for sand and aggregate; see our substrate depth guide for how depth is chosen.
FAQ
How much substrate does a 60 cm tank need?
At the default 5 cm depth on a 60 × 30 cm floor: 9 L — 14.4 kg sand, 13.5 kg gravel or 7.2 kg aquasoil. Sloping? Use the average depth.
How deep should the substrate be?
For plants, commonly 5–7.5 cm (2–3 in) so roots can establish; fish-only tanks are fine under 5 cm (2 in); quarantine and hospital tanks often go bare. The trade-offs — including why very deep sand can go anaerobic — are covered in the depth guide.
How heavy is a litre of sand?
About 1.6 kg dry and bulk-packed. A 9 L sand bed is roughly 14.4 kg — worth knowing before you put it on the third floor of a wobbly stand.
Does substrate reduce my tank's water volume?
Yes — 9 L of substrate is 9 L not holding water. Enter the same dimensions in the volume calculator and subtract, or simply dose by measured real water volume.
Example: planted-tank substrates (affiliate concept)
Once the calculator tells you how many litres you need, this is where we would list substrates that ship in sensible bag sizes.
Check price →Heuristic, not gospel
The geometry is exact; the densities are approximations and substrates vary by brand and grading. If a manufacturer prints a litres-per-bag figure, trust that over our generic weight estimate. And rinse as directed — cloudiness aside, some soils are pre-charged with ammonia and interact with your nitrogen cycle from day one.