How the aquarium gravel calculator works
Gravel needed depends on the tank’s footprint (length × width) and the depth you want, not on the number of gallons.
- Volume = length × width × depth, all in inches, gives cubic inches.
- Cubic feet = cubic inches ÷ 1,728.
- Pounds = cubic feet × about 100. Aquarium gravel and sand both weigh close to 100 pounds per cubic foot.
Example. A 40 gallon breeder is 36 × 18 inches. At 2 inches deep: 36 × 18 × 2 = 1,296 cubic inches = 0.75 cubic feet, so about 75 pounds of gravel.
Gravel by tank size
| Tank (footprint) | Per inch of depth | 2 in deep | 3 in deep |
|---|---|---|---|
| 10 gallon (20 × 10 in) | 12 lb | 23 lb | 35 lb |
| 20 gallon high (24 × 12 in) | 17 lb | 33 lb | 50 lb |
| 20 gallon long (30 × 12 in) | 21 lb | 42 lb | 63 lb |
| 29 gallon (30 × 12 in) | 21 lb | 42 lb | 63 lb |
| 40 gallon breeder (36 × 18 in) | 38 lb | 75 lb | 113 lb |
| 55 gallon (48 × 13 in) | 36 lb | 72 lb | 108 lb |
| 75 gallon (48 × 18 in) | 50 lb | 100 lb | 150 lb |
| 125 gallon (72 × 18 in) | 75 lb | 150 lb | 225 lb |
Footprints vary a little between manufacturers. Measure the inside of your tank if you want an exact figure.
Gravel, sand or plant substrate?
| Substrate | Weight | Notes |
|---|---|---|
| Aquarium gravel | About 100 lb per cu ft | Easy to vacuum; good for most community tanks |
| Aquarium sand | About 100 lb per cu ft | Natural look, suits bottom dwellers; keep it shallower |
| Plant substrate / aqua soil | Often roughly half the weight of gravel | Sold by volume (litres) as often as by weight; check the bag |
For lightweight plant soils, use the litres figure from the calculator and compare it with the litres printed on the bag.
Before you add gravel
- Rinse it. New gravel carries dust that clouds the water. Rinse in a bucket until the water runs mostly clear.
- Check the weight on the stand. Gravel adds a lot on top of the water. A full 55 gallon tank already weighs several hundred pounds.
- Slope it. A deeper back and shallower front looks good and helps debris collect where you can vacuum it.
This calculator is for aquariums. For landscaping gravel by the cubic yard or ton, use the main gravel calculator.
Questions people ask
- How much gravel do I need for a 20 gallon tank?
- For a 20 gallon long (30 × 12 in footprint), about 21 pounds per inch of depth, so about 42 pounds for 2 inches. A 20 gallon high (24 × 12 in) needs about 17 pounds per inch.
- How much gravel for a 55 gallon tank?
- A standard 55 gallon tank (48 × 13 in) needs about 36 pounds per inch of depth, so roughly 72 pounds for 2 inches.
- Is the rule of 1 pound per gallon right?
- It is a rough guide for about an inch of gravel in a standard tank. It is off for tall or shallow tanks, because the footprint, not the number of gallons, decides how much gravel you need.
- How deep should aquarium gravel be?
- About 1 to 2 inches for most fish-only tanks, and 2 to 3 inches where you will grow rooted plants. Many keepers slope it deeper at the back.