Aquarium substrate calculator

Calculate gravel, sand or planted-tank soil volume for a flat or sloped bed, and how many bags to buy.

Formula

Substrate volume = length × width × average depth, where average depth = (front depth + back depth) ÷ 2 for a straight slope. Inches³ ÷ 231 × 3.785 gives liters; cm³ ÷ 1,000 gives liters. 1 cubic foot = 28.32 L; 1 US dry quart = 1.101 L.

Bags sold by weight

Gravel, sand and aquasoil differ a lot in density, so a pound count can’t be calculated from volume alone. If the label gives a volume, use it. If it only gives weight, weigh a measured container of the product (or find the bulk density on the maker’s site) and enter that density.

Worked example

A 30 × 12 inch footprint sloped from 1.5 in at the front to 3 in at the back has an average depth of 2.25 in: 30 × 12 × 2.25 = 810 in³ ≈ 13.3 L (0.47 ft³), or two 10-liter bags.

Sources

NIST Special Publication 811, Appendix B.8 (conversion factors)