Aquarium Substrate Calculator
Calculate how many pounds of sand or gravel substrate you need for an aquarium from its footprint and desired substrate depth.
How this calculator works
Substrate volume comes from the tank’s footprint — length times width — multiplied by how deep you want the substrate layer, all measured in inches. Dividing by 1,728, the number of cubic inches in a cubic foot, converts that figure to cubic feet, which is then multiplied by the substrate’s density to get a weight in pounds.
Formula: Substrate volume (cu ft) = (tank length × width × substrate depth, all in inches) ÷ 1,728. Weight = volume × density (about 100 lb per cubic foot for sand).
Worked example
- Tank footprint: 48 in × 18 in, with a 2-inch substrate depth
- Volume: (48 × 18 × 2) ÷ 1,728 = 1,728 ÷ 1,728 = 1.0 ft³
- Weight at 100 lb/cu ft (sand): 1.0 × 100 = 100.0 lb
Notes
A planted tank usually calls for a deeper substrate bed, often in the 2-3 inch range, to give root systems room to establish, compared with a simple gravel-bottom fish-only tank, which can get by with under 1 inch of substrate.
Gravel is also somewhat lighter than sand per cubic foot, so this calculator defaults to sand’s typical density. If you’re using gravel or a specialty planted-tank substrate, adjust the density input to match your product’s actual weight per cubic foot for a more accurate order.
How to use
Measure your tank’s footprint — length and width — in inches, decide how deep you want the substrate layer, and enter your substrate’s density if it’s not standard sand. The calculator returns the volume in cubic feet and the total weight in pounds so you know how much to buy.
Density varies by substrate type (sand, gravel, planted-tank soil) — check your specific product’s coverage rate for an exact order.
Frequently asked questions
How deep should my aquarium substrate be?
It depends on what the tank is for. A fish-only tank with a bare gravel bottom can work with a thin layer, while a planted tank generally wants a deeper bed so root systems have room to establish and anchor. Check your specific plant species' rooting needs, since heavy root feeders want more depth than shallow-rooting plants.
Why does the calculator default to sand's density instead of gravel's?
Sand is denser than gravel per cubic foot because its finer grains pack together more tightly with less air space between pieces. The calculator uses sand's typical density as the default starting point, but you can adjust the density input to match gravel or a specialty substrate if that's what you're using.
Does substrate weight affect my tank's total water weight or stand requirements?
Yes — substrate adds to the total load your aquarium stand has to support, on top of the water, glass, and equipment. When planning a stand or checking a floor's load capacity, add the substrate's weight to your tank's water weight rather than treating the substrate as negligible.
Why does the formula divide by 1,728?
1,728 is the number of cubic inches in one cubic foot (12 × 12 × 12). Since tank footprint and substrate depth are measured in inches, multiplying them together gives a volume in cubic inches, and dividing by 1,728 converts that figure into cubic feet so it can be multiplied by a density given in pounds per cubic foot.
Estimates only. Verify quantities with your supplier before purchasing.