About this tool
The Aquarium Substrate Calculator is a free, in-browser tool that tells you how much gravel, sand or aquasoil you need to cover a tank's bottom to a chosen depth — and how many bags that means at your bag size. Buying by guess usually leaves you short or with wasted product; this sizes it precisely. Everything runs locally in your browser.
The method finds the substrate volume as footprint × depth: V (cm³) = length_cm × width_cm × depth_cm, converted to liters (÷ 1000). Weight = volume in liters × the material's bulk density in kg/L: fine gravel 1.6, coarse gravel 1.5, aquarium sand 1.5, play sand 1.6, aquasoil/ADA 0.8, crushed coral 1.4, eco-complete 1.4. Weight converts between kilograms and pounds (1 kg = 2.2046 lb), and if you enter a bag size the tool rounds up to whole bags. A depth of about 2–3 cm (0.8–1.2 in) suits non-planted tanks, while rooted plants want a deeper 5–8 cm (2–3 in) bed for the roots.
As a worked example, a 90 × 45 cm tank floor at 5 cm of fine gravel is 90 × 45 × 5 = 20,250 cm³ = 20.25 L, and at 1.6 kg/L that is about 32.4 kg (roughly 71.4 lb) — so about four 9 kg bags. Aquasoil is much lighter than gravel for the same volume because its density is only 0.8 kg/L, so don't size lightweight planted substrates by a gravel weight chart.