Substrates differ in weight a lot: aquarium sand is heavy, crushed coral lighter, and the clay-based soils for planted tanks lighter still. So the calculator works from each one's weight per volume rather than one rule for all.
How to use this calculator
- Choose the substrate.
- Measure the inside length and width of the tank.
- Enter the depth of the bed. In a planted tank, use the average if you slope it from back to front.
Worked examples
Gravel for a long tank
Substrate: Aquarium gravel · Tank: 30 × 12 in · Bed depth: 2 in
- Substrate
- 39 lb
- 20 lb bags
- 2
- Bed volume
- 3.1 US gallons
Sand for a large community tank
Substrate: Aquarium sand · Tank: 48 × 13 in · Bed depth: 1.5 in
- Substrate
- 54 lb
- 20 lb bags
- 3
- Bed volume
- 4.1 US gallons
Aragonite sand for a reef tank
Substrate: Aragonite reef sand · Tank: 36 × 18 in · Bed depth: 2 in
- Substrate
- 75 lb
- 20 lb bags
- 4
- Bed volume
- 5.6 US gallons
Fluval Stratum for a planted tank
Substrate: Fluval Stratum · Tank: 36 × 18 in · Bed depth: 3 in
- Substrate
- 70 lb
- Bed volume
- 8.4 US gallons
Seachem Flourite for a small tank
Substrate: Seachem Flourite · Tank: 24 × 12 in · Bed depth: 2 in
- Substrate
- 21 lb
- 15.4 lb bags of Flourite
- 2
- Bed volume
- 2.5 US gallons
How the amount is worked out
The bed is a flat box: length times width times depth, in inches, divided by 1,728 gives cubic feet. Multiply by the substrate's weight per cubic foot and you have the pounds. That is the method CaribSea gives for a precise figure.
The quick rule is 1 to 2 lb per gallon per gallon of tank. It is handy for a guess, but a tall tank needs less than its gallons suggest and a long, shallow one more, so measuring is better.
Weight of common substrates
- Natural aquarium gravel: about 93 lb per cubic foot.
- Aquarium sand: about 100 lb per cubic foot.
- Aragonite reef sand: about 100 lb per cubic foot.
- Crushed coral: about 75 lb per cubic foot.
- Fluval Stratum: Fluval works it out as 1 kg per liter of bed.
- Seachem Flourite: one bag of 15.4 lb fills about 425 cubic inches.
Bags to buy
Gravel and sand often come in bags of 20 lb, and the calculator rounds up to whole bags of that size. Flourite is counted by its own bag. Rinse gravel and sand before they go in, unless the bag says not to: some live sands and planted-tank soils should go in as they are.
Common questions
How much gravel do I need for my aquarium?
Multiply the inside length, width and depth of the bed in inches, divide by 1,728 and multiply by the gravel's weight per cubic foot, about 93 lb per cubic foot for natural gravel. The calculator does it and counts the bags.
How many pounds of sand per gallon?
The quick rule is 1 to 2 lb per gallon per gallon, depending on how deep you want it. Measuring the tank gives a better answer, because tanks of the same gallons can have very different floor areas.
Is sand heavier than gravel?
Usually a little: aquarium sand is about 100 lb per cubic foot and natural gravel about 93 lb per cubic foot, so the same bed of sand takes a few more pounds.
How much substrate does a planted tank need?
Planted-tank soils are lighter than gravel, so they are worked out by volume. Fluval counts 1 kg per liter of bed for Stratum. Many planted tanks slope the bed deeper at the back, so enter the average depth.