Aquarium substrate calculator
Enter the inside footprint and the depth you want at the front and back. The calculator returns weight, volume and the number of bags.
The formula
substrate volume = length × width × average depth, and weight = volume × bulk density. Measure the inside of the tank. For a sloped bed, the average depth is (front depth + back depth) ÷ 2.
| Substrate | Bulk density | Per inch over 1 ft² |
|---|---|---|
| Aquarium gravel | 1.6 kg/L (100 lb/ft³) | 8.3 lb |
| Sand (silica, pool filter) | 1.55 kg/L | 8.1 lb |
| Aragonite reef sand | 1.45 kg/L | 7.5 lb |
| Aqua soil | ≈ 1.0 kg/L (sold by liters) | 2.4 L |
How deep should substrate be?
- Fish-only tanks: 1–2 inches (2.5–5 cm) of gravel or sand is easy to clean.
- Planted tanks: 2–3 inches (5–7.5 cm), sloping to 3–4 inches at the back for root feeders and depth.
- Corydoras and loaches: fine, rounded sand so they can sift without damaging their barbels.
- Reef tanks: a shallow sand bed of 0.5–1.5 inches, or a deep sand bed of 4 inches or more for denitrification.
The old "1 lb of gravel per gallon gives 1 inch" rule only works for standard-proportion tanks. A 20-gallon high and a 20-gallon long hold the same water but the long tank has 25% more floor, so it needs 25% more gravel. Read the full substrate guide.
FAQ
How much sand do I need for a 20-gallon long tank?
About 20 lb per inch of depth: a 30 × 12 inch footprint at 2 inches deep needs roughly 40 lb of sand or gravel.
How much gravel do I need for a 55-gallon tank?
About 35 lb per inch of depth over the inside footprint, so roughly 70 lb for a 2-inch bed.
How many bags of aqua soil do I need?
Aqua soil is sold by volume. Multiply inside length × width × depth in centimeters and divide by 1,000 for liters, then divide by the bag size in liters.