How much substrate do I need?
Substrate volume is the tank footprint × the average depth. For a slope from front to back, the average of the two depths is used:
volume = length × width × (front depth + back depth) ÷ 2
Weight is volume × bulk density. Bulk density is the weight of a liter of the loose material, including the air between grains, and varies by product:
- Sand: roughly 1.5–1.7 kg per liter
- Gravel: roughly 1.4–1.6 kg per liter
- Aquasoils: often around 0.8–1.1 kg per liter
Many aquasoils are sold by volume (liters) rather than weight; in that case use the volume result directly. Check the bag for the manufacturer's figure.
Typical depths
- Fish-only tanks: about 1–2 inches (2.5–5 cm).
- Planted tanks: about 2–3 inches (5–8 cm), deeper at the back for a sense of depth.
Rule of thumb
For sand or gravel, about 1 lb per gallon of tank volume gives roughly an inch of substrate in standard tanks; 2 lb per gallon gives about 2 inches. The calculator is more precise because it uses the actual footprint.
Frequently asked questions
How much sand for a 20 gallon long tank?
A 20 long (30 × 12 in) with 2" of sand needs 720 cubic inches, about 11.8 liters, or roughly 42 lb of sand.
How deep should aquarium substrate be?
About 1–2 inches for most fish-only tanks and 2–3 inches for planted tanks with rooted plants, often sloping deeper toward the back.