Aquarium gravel and sand calculator
Find out how much gravel, sand, aquasoil or crushed coral your fish tank needs. Enter the tank's length and width and the depth you want. You'll see the volume, the weight and how many bags to buy.
Your tank and substrate
Some makers list it as "average density". Most gravel and sand is 90–100 lb/ft³ (1.45–1.6 kg/L).
Usual depth for gravel: 1.5–2 in (4–5 cm). Enter the same depth twice for a flat bed, or a bigger number at the back for a slope.
Your own bag size, or the depth from what you have
You need
23.1 lb
of gravel (10.5 kg) for an average depth of 2 in (5.1 cm).
Bags to buy
| Bag size | Bags | Total |
|---|---|---|
| 5 lb (2.3 kg) | 5 | 25 lb |
| 10 lb (4.5 kg) | 3 | 30 lb |
| 20 lb (9.1 kg) | 2 | 40 lb |
| 25 lb (11.3 kg) | 1 | 25 lb |
| 50 lb (22.7 kg) | 1 | 50 lb |
Rounded up to whole bags. Weights are for dry substrate and vary a little by product, so check the bag.
How much gravel do you need? Multiply the tank's inside length × width × substrate depth to get the volume, then multiply by the substrate's weight per volume: about 1.6 kg per litre (100 lb per cubic foot) for gravel. In inches, pounds of gravel ≈ length × width × depth ÷ 17.3, so a 10 gallon tank (20 × 10 in) needs about 23 lb for a 2 inch bed.
How the calculator works
- Average depth = (depth at the front + depth at the back) ÷ 2. A straight slope from front to back makes a wedge, so the average gives the exact volume.
- Volume = length × width × average depth. In inches, multiply cubic inches by 0.016387 to get litres (1 in³ = 16.387 cm³). In centimetres, divide cubic centimetres by 1,000.
- Weight = litres × bulk density in kg per litre. Divide kilograms by 0.4536 to get pounds.
- Bags = weight (or litres for aquasoil) ÷ bag size, always rounded up.
Bulk density is the weight of a loose, dry pile including the gaps between grains, which is why it is lower than the weight of solid rock.
Worked example
A 20 gallon long is 30 × 12 in. You want gravel sloped from 1.5 in at the front to 2.5 in at the back.
- Average depth: (1.5 + 2.5) ÷ 2 = 2 in
- Volume: 30 × 12 × 2 = 720 in³ = 11.8 litres (0.42 ft³)
- Weight: 11.8 L × 1.6 kg/L = 18.9 kg = 41.6 lb
- Bags: 41.6 ÷ 20 = 2.08, so 3 bags of 20 lb, or 2 bags of 25 lb
Weight and depth by substrate type
| Substrate | Usual depth | Weight per volume | Pounds from inches |
|---|---|---|---|
| Aquarium gravel | 1.5–2 in (4–5 cm) | 1.6 kg/L (100 lb/ft³) | L × W × D ÷ 17.3 |
| Sand | 1–2 in (2.5–5 cm) | 1.55 kg/L (97 lb/ft³) | L × W × D ÷ 17.9 |
| Aquasoil (planted tanks) | 2–3 in (5–7.5 cm) average | 1 kg/L (62 lb/ft³), estimate | L × W × D ÷ 27.7 |
| Crushed coral | 1–2 in (2.5–5 cm) | 1.15 kg/L (72 lb/ft³) | L × W × D ÷ 24.1 |
| Aragonite sand | 1–2 in (2.5–5 cm) | 1.45 kg/L (91 lb/ft³) | L × W × D ÷ 19.1 |
Gravel and sand densities are typical published values for aquarium products and dry sand and gravel. Aquasoil is sold by the litre and its weight is rarely printed, so treat its weight as a rough guide and buy by volume.
How much gravel and sand for standard tank sizes
Based on the usual outside length and width of each standard tank, so the figures include a small margin for the glass. Aquasoil is sloped from 2 in at the front to 3 in at the back.
| Tank | Footprint | Gravel, 2 in | Sand, 1.5 in | Aquasoil, 2–3 in |
|---|---|---|---|---|
| 3 gallon | 12 × 8 in | 11 lb (5 kg) | 8 lb (3.7 kg) | 3.9 L |
| 5 gallon | 16 × 8 in | 15 lb (6.7 kg) | 11 lb (4.9 kg) | 5.2 L |
| 10 gallon | 20 × 10 in | 23 lb (10.5 kg) | 17 lb (7.6 kg) | 8.2 L |
| 15 gallon | 24 × 12 in | 33 lb (15.1 kg) | 24 lb (11 kg) | 11.8 L |
| 20 gallon | 24 × 12 in | 33 lb (15.1 kg) | 24 lb (11 kg) | 11.8 L |
| 20 gallon long | 30 × 12 in | 42 lb (18.9 kg) | 30 lb (13.7 kg) | 14.7 L |
| 29 gallon | 30 × 12 in | 42 lb (18.9 kg) | 30 lb (13.7 kg) | 14.7 L |
| 40 gallon | 36 × 18 in | 75 lb (34 kg) | 54 lb (24.7 kg) | 26.5 L |
| 55 gallon | 48 × 13 in | 72 lb (32.7 kg) | 52 lb (23.8 kg) | 25.6 L |
| 75 gallon | 48 × 18 in | 100 lb (45.3 kg) | 73 lb (32.9 kg) | 35.4 L |
| 125 gallon | 72 × 18 in | 150 lb (68 kg) | 109 lb (49.4 kg) | 53.1 L |
A 20 gallon long and a 29 gallon share the same 30 × 12 in floor, so they need the same amount of substrate. Height doesn't matter, only the floor area.
Tips before you buy
- Measure inside the glass. Outside measurements include the glass and frame, so they overestimate a little. That is a small safety margin, not a problem.
- Plan for hardscape. Rocks and wood sitting on the glass replace some substrate, but hills and terraces use more. If you are building slopes, buy one extra bag.
- Rinse gravel and sand, not aquasoil. Rinse gravel and sand until the water runs clear. The aquasoil instructions we checked say not to rinse it, because the granules crumble and cloud the water.
- New aquasoil can release ammonia. Nutrient-rich soils can push ammonia and nitrite up right after setup. Test the water and wait for both to read zero before adding fish or shrimp. Our guides explain the nitrogen cycle.
- Crushed coral and aragonite change your water. They slowly dissolve and raise pH, KH and GH. That suits hard-water fish such as African rift lake cichlids, but not soft-water fish. Check each species' pH range in our fish database.
- Plain gravel and sand can grow plants. Rooted plants do well in them with root fertilizer tabs. Aquasoil is most useful for carpeting plants and heavily planted layouts.
- Substrate is heavy. A 75 gallon tank with 2 in of gravel carries about 100 lb (45 kg) of it. Add it to the water weight with the aquarium weight calculator before you choose a stand.
Related calculators
- Aquarium volume calculator: Work out how many gallons or litres your tank holds, for rectangular, cylinder, bow front, corner and hexagon tanks.
- Aquarium weight calculator: Estimate the full weight of your aquarium with water, glass, substrate and rock, so you can check your stand and floor.
- Aquarium CO2 calculator (pH and KH): Estimate dissolved CO2 in a planted tank from your pH and KH readings.
- Aquarium unit converter: Convert gallons and litres, Fahrenheit and Celsius, inches and centimetres, and dGH, dKH and ppm.
- Fish tank stocking calculator: check how many fish your tank can hold and whether they get along.
- Tank size guides: dimensions, weight and fish ideas for each standard tank.
- All aquarium calculators
Shop for this
- Aquarium gravel (opens Amazon in a new tab)Smooth gravel about 2 in (5 cm) deep. Use the substrate calculator for the exact amount. How to choose
- Aquarium sand (opens Amazon in a new tab)Soft sand for corydoras, loaches and other bottom diggers. How to choose
- Aquasoil for planted tanks (opens Amazon in a new tab)Feeds plant roots, but softens water and lowers pH. How to choose
Product links go to Amazon search results. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Disclosure.
Frequently asked questions
How much gravel do I need for a 10 gallon tank?
About 12 lb for each inch of depth. A standard 10 gallon tank is 20 × 10 in, so a 2 inch bed takes about 23 lb (10.5 kg) of gravel. For 1.5 inches of sand you need about 17 lb.
Is "1 pound of gravel per gallon" right?
Only for some tanks. It gives roughly a 1 inch bed in a 10 gallon or a 20 gallon long, but taller tanks have less floor per gallon. A 55 gallon (48 × 13 in) needs only about 36 lb for 1 inch, which is 0.66 lb per gallon. Work from the length and width instead, as this calculator does.
How deep should aquarium substrate be?
About 1.5–2 in (4–5 cm) of gravel or 1–2 in (2.5–5 cm) of sand suits most tanks. Planted tanks with aquasoil usually average 2–3 in (5–7.5 cm), sloped deeper at the back for roots. Thinner beds are fine for fish-only tanks. Deep, fine sand needs stirring so it does not pack down.
How many bags of aquasoil do I need?
Aquasoil is sold by volume, so work in litres. One maker sizes its 9 litre bag for a 60 × 30 cm tank, which is about 5 cm (2 in) deep. A 20 gallon long (30 × 12 in) sloped from 2 in to 3 in needs about 14.7 litres, so 2 bags of 9 litres.
Is sand heavier than gravel?
For the same volume they are close. Most aquarium sands and gravels weigh about 90–100 lb per cubic foot (1.45–1.6 kg per litre). Crushed coral (about 72 lb per cubic foot) and aquasoil (roughly 1 kg per litre) are lighter, so the same depth weighs less.
Sources
- CaribSea. Freshwater substrates: average density of aquarium sands and gravels (92–100 lb/ft³) and porous planted gravel (54 lb/ft³).
- CaribSea. Marine substrates: crushed coral (72 lb/ft³) and aragonite sands (85–96 lb/ft³).
- The Engineering ToolBox. Dirt and mud densities: dry gravel 105 lb/ft³, dry sand 97 lb/ft³.
- The Engineering ToolBox. Densities of common materials: dry dirt 65–80 lb/ft³, used with porous planted gravel to estimate aquasoil.
- ADA (Aqua Design Amano). Aqua Soil Amazonia Ver.2 instructions (PDF): one 9 L bag for a 60 × 30 cm tank, no rinsing, ammonia and nitrite after setup. Bag sizes from the Aqua Soil product page.
- Ultum Nature Systems. Controsoil application guide: 10 L for a 60 × 30 cm tank.
- NIST. Guide to the SI, Appendix B.9: inch, pound, cubic foot and quart conversion factors.