Aquarium Substrate Calculator
Built by Johnny Alto · free, no sign-up · updated July 26, 2026
Enter your tank's footprint and how deep you want the substrate to find how many pounds and kilograms of gravel, sand, or aqua soil to buy. A depth of 1 to 2 inches suits most tanks, while rooted plants do better with 2 to 3 inches.
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Densities vary by brand and grain size, so treat this as a close estimate and round up when buying. Gravel and sand are heavy (roughly 1.5 to 1.6 g/cm3); aqua soil is lighter and more porous.
How much substrate do you need?
Substrate is sized by the footprint of the tank, not its total volume, because it sits in an even layer on the bottom. Multiply the tank's length by its width by the depth you want to get the volume of substrate, then multiply by the material's density to get weight. This calculator does that for you and gives the answer in both pounds and kilograms.
Gravel and sand are dense, at roughly 1.5 to 1.6 grams per cubic centimeter, so they add up quickly. Aqua soil is lighter and more porous, so the same depth weighs less. Brands and grain sizes vary, so round up rather than coming up short.
How deep should aquarium substrate be?
One to two inches is plenty for a fish-only tank and makes gravel-vacuuming easy. For a planted tank, aim for two to three inches so roots have room to anchor and spread. Deeper than that traps waste and can go anaerobic without root systems to keep it healthy.
Recommended gear
Substrate and cleaning gear
Frequently asked questions
How much substrate do I need for a 20 gallon aquarium?
A standard 20 gallon tank has a 24 by 12 inch footprint. At a 2 inch depth that is about 33 pounds of gravel or sand, or roughly 15 kilograms.
How deep should the substrate be?
Use 1 to 2 inches for a fish-only tank and 2 to 3 inches for a planted tank so roots can anchor. Going much deeper can trap waste.
Does gravel or sand weigh more?
They are close, with gravel around 1.6 grams per cubic centimeter and sand around 1.5, so the same depth of gravel weighs slightly more.
How much aqua soil do I need?
Aqua soil is lighter and more porous than gravel, so the same footprint and depth weighs noticeably less. Buy by liters if the brand lists it, and use this estimate as a cross-check.
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This calculator gives estimates for planning only; always confirm against your own measurements and species research. Some links are to our buying guides, which contain affiliate links. As an Amazon Associate I earn from qualifying purchases.
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