Aquarium Sand & Substrate Calculator (Pounds Needed)

How it works

The bed is a box: the length and width of the tank floor times the depth you want. Its weight is that volume times how heavy the material is per cubic foot.

volume (ft³)  = length (in) × width (in) × depth (in) ÷ 1,728
weight (lb)   = volume × bulk density (lb per ft³)
to buy (lb)   = weight × (1 + extra allowance)

Bulk density is what a cubic foot of loose, dry material weighs. We use CaribSea’s published values: 100 lb/ft³ for aragonite and cichlid sands, 85 for Special Grade reef sand, 80 for Eco-Planted, 75 for crushed coral and gravel. Quartz sand is 11.7 lb per gallon of volume (Reef Exclusive), about 87.5 lb/ft³.
Use inside dimensions. The glass takes a few tenths of an inch off each side.
A gentle slope is fine. Enter the average depth, for example 1 inch at the front and 3 inches at the back is about 2 inches.
In metric, the same calculation works in litres and kilograms: bulk density of 100 lb/ft³ is about 1.6 kg per litre.

Worked example

A 55 gallon tank, 48 inches long and 13 inches wide, with a 2 inch aragonite bed:

Volume: 48 × 13 × 2 ÷ 1,728 = 0.722 ft³
Weight: 0.722 × 100 = 72.2 lb
With 10% extra: about 79 lb, which is two 40 lb bags.

Tips from the fish room

Keep the top of the bed level with a card. A bed that looks 2 inches deep at the front can be much deeper at a corner after you add rock.
Put rock on the glass, not on the sand. Sand shifts under heavy rockwork, and a burrowing fish can topple a stack.
Mind the weight. Sand is heavy. The aquarium weight calculator adds it to the total your stand has to carry.
Go slowly when you add water. Pour onto a plate or a bag on the bed so you don’t crater it.

FAQ

How much sand do I need for a 55 gallon tank?

For a standard 48 × 13 inch tank, a 2 inch bed takes about 72 lb of aragonite or aquarium sand, or about 79 lb with a 10% allowance. A 1 inch bed takes about half that.

Is it really 1 pound per gallon for every inch of depth?

Only for some tanks. The rule works for a 20 gallon long (30 × 12 inches), where 1 inch of sand is about 21 lb, or roughly 1 lb per gallon. Slimmer tanks such as a 55 gallon need less per gallon, and wide, shallow tanks need more. Use the real length and width instead of the gallon rule.

How deep should the sand or gravel be?

Retailers commonly suggest 1–2 inches for a standard reef bed, 2–3 inches for planted freshwater tanks so roots can anchor, and 3–4 inches or more for a deep sand bed, which needs more maintenance.

Why does the calculator add 10% extra?

Rockwork sits on the glass or on the sand and displaces some of it, and bags settle and spill. Reef Exclusive suggests 10–15% extra. Set the box to 0 if you want the exact bed weight.

Does wet sand weigh more than the number shown?

Yes. The densities here are for dry material. Damp sand holds water in the gaps and weighs more on the way in, so count the bag weight, not the wet weight, when you buy.

Sources

Frequently asked questions, "How much substrate do I need?", CaribSea. Pounds = length × width × bed depth (inches) ÷ 1,728 × the product's bulk density. Densities from 75 to 100 lb per cubic foot; general rule of 1 to 2 pounds per gallon.
Reef Sand & Substrate Calculator, Reef Exclusive. Aragonite about 13.9 lb and quartz sand 11.7 lb per gallon of bed volume; add 10–15% extra.

Formula and sources last checked September 30, 2026. How we test formulas.

How it works

Worked example

Tips from the fish room

FAQ

Sources

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