Aquarium Substrate Calculator
Short answer: a 20 gallon long tank needs about 42 lb (19 kg) of gravel for a 2 inch average bed, before extra for waste. Use this aquarium substrate calculator to get the exact weight, bags and cost for your own tank in under a minute.
Extra: waste, bags and cost (optional)
0 lb / 0 kg
Total to buy for your tank, including extra for waste.
What does this aquarium substrate calculator do?
This free tool works out how much substrate your tank needs. It shows the volume in litres and the weight in pounds and kilograms. Use it for a planted aquarium, a fish-only tank or a sand bed.
Type in the length and width of your tank, then the depth you want. Pick gravel, sand, aqua soil, crushed coral or a custom substrate. You get the amount to buy, the number of bags and the cost.
It also works as a gravel calculator in kg. Enter your tank size and your preferred depth, and read the kilograms of gravel you need. Rectangular, bow-front, hexagon, round and corner tanks are all covered.
Not sure what depth to use? For sand, I suggest 1 to 2 inches (2.5 to 5 cm) in most tanks. For gravel and aqua soil, 2 to 3 inches (5 to 7.5 cm) works well.
One thing to remember: substrate takes up space, so your tank will hold a little less water than its label says. This calculator does not work out that water loss.
How this aquarium substrate calculator works
I built this tool for beginners, so it is simple. Pick your tank shape and type in its size, or tap a common tank from the list.
Next, choose gravel, sand, aqua soil, crushed coral or your own custom substrate. The calculator fills in a safe depth for you.
Then read your result: weight in lb and kg, litres, bags and cost. The compare list shows the same tank with every substrate. Tap Download PDF to save it for the shop.
The math is volume (area x average depth) times the weight of one litre of that substrate. Gravel and sand are about 1.6 kg per litre. Crushed coral is about 1.4 kg per litre. Aqua soil is lighter, at about 0.95 kg per litre. Brands vary, so check your bag label, or use Custom to enter your own number.
How much substrate do I need for my tank?
This chart shows gravel for an average depth of 2 inches (5 cm). Weights are rounded and do not include extra for waste. Use the calculator above for sand, soil, coral or a deeper bed.
| Tank | Floor size | Gravel needed |
|---|---|---|
| 5.5 gallon | 16 x 8.5 in | about 16 lb (7 kg) |
| 10 gallon | 20 x 10 in | about 23 lb (10.5 kg) |
| 20 gallon high | 24 x 12 in | about 33 lb (15 kg) |
| 20 gallon long | 30 x 12 in | about 42 lb (19 kg) |
| 29 gallon | 30 x 12 in | about 42 lb (19 kg) |
| 40 gallon breeder | 36 x 18 in | about 75 lb (34 kg) |
| 55 gallon | 48 x 13 in | about 72 lb (33 kg) |
| 75 gallon | 48 x 18 in | about 100 lb (45 kg) |
How much substrate per gallon?
A quick rule: plan on about 1 lb of gravel or sand per gallon for every 1 inch of depth. In real tanks it runs from about 0.7 lb per gallon in big tanks to about 1.4 lb in tiny ones.
A 2 inch bed in a 20 gallon long tank is about 42 lb. Because tank shape changes the answer, the calculator is more accurate than any rule.
How thick should aquarium substrate be?
| Type | Good depth | Best for |
|---|---|---|
| Gravel | 2-3 in (5-7.5 cm) | Most fish tanks and easy plants |
| Sand | 1-2 in (2.5-5 cm) | Corydoras, loaches and a natural look |
| Aqua soil | 2-3 in (5-7.5 cm) | Planted tanks with root feeders |
| Crushed coral | 1-2 in (2.5-5 cm) | Hard, high-pH tanks such as African cichlids |
A slope that is deeper at the back and thinner at the front looks natural and gives plants more room. That is why the calculator has a front and a back depth.
Sand vs gravel vs aqua soil vs crushed coral
Gravel is easy to clean and lets water flow through. Sand is soft for bottom feeders, but keep it thin. Aqua soil feeds plants, but it is light and breaks down over time.
Crushed coral slowly raises pH and water hardness. It suits African cichlids and brackish tanks. Avoid it with soft-water fish and many planted tanks.
Substrate for hexagon, bow-front, round and corner tanks
Many calculators only do rectangles. This one also handles bow-front, hexagon, round and quarter-round corner tanks. Bow-front and corner results are close estimates, so add a little extra if your tank has odd curves.
Substrate mistakes to avoid
- Do not skip rinsing gravel, sand and crushed coral. Dust makes the water cloudy. Do not rinse aqua soil, because it turns to mud.
- Do not pile sand too deep. A thick sand bed can trap gas pockets in some tanks.
- Do not forget the weight. Water is about 8.3 lb per US gallon, and substrate adds more. Check that your stand can take it.
- New aqua soil can release ammonia at first. Do small water changes and test the water.
Aquarium substrate FAQ
How do I calculate how much substrate I need?
Multiply the floor area by the average depth to get the volume. Then multiply by the weight of one litre of your substrate. For a 30 x 12 in floor with 2 in of gravel, that is about 11.8 litres, or 18.9 kg (41.6 lb). An aquarium substrate calculator does these steps for you.
How much gravel do I need for a 20 gallon tank?
A 20 gallon long tank (30 x 12 in) needs about 42 lb of gravel for a 2 inch average depth. A 20 gallon high (24 x 12 in) needs about 33 lb.
How much substrate do I need per gallon?
About 1 lb per gallon for each inch of depth. It runs from about 0.7 lb in big tanks to 1.4 lb in tiny ones, so use the calculator for your exact size.
How thick should substrate be in a planted tank?
Aim for 2 to 3 inches (5 to 7.5 cm) of gravel or aqua soil. Make it a little deeper at the back.
How much sand do I need for a 10 gallon tank?
A 10 gallon tank (20 x 10 in) needs about 12 lb for a 1 inch layer and about 17 lb for 1.5 inches.
How much substrate do I need for a 60 litre tank?
For a 60 x 30 cm floor with a 5 cm average depth, you need about 9 litres, or roughly 14 kg of gravel (about 15 kg with the default 5% extra). Switch the calculator to cm and kg to check your exact size.
Is crushed coral good for a freshwater aquarium?
It is good for hard-water fish such as African cichlids, because it slowly raises pH and hardness. It is a poor choice for soft-water fish and many planted tanks.
Can I use a substrate that is not on the list?
Yes. Choose Custom, type the weight per litre from the bag label, and the calculator does the rest.
How many bags of substrate should I buy?
Open the extra, bags and cost section, type your bag size, and the calculator rounds up to whole bags for you.
Do I need to rinse aquarium gravel and sand?
Yes, rinse gravel and sand until the water runs fairly clear. Do not rinse aqua soil.
Does it work for hexagon or bow-front tanks?
Yes. Choose the shape at the top and enter its measurements. Results for curved tanks are close estimates.
Next step: check if your tank is overstocked with my aquarium fish stocking calculator.
Written and tested by Anil Satak, M.Sc. Zoology, FishioHub. Results are estimates. Densities vary by brand, so check your product label.