How Much Aquarium Substrate Do You Need? About 11 kg of Gravel for a 60 cm Tank, and How Many Litres of Soil: Chart by Depth
When buying substrate, many people get stuck on how many bags to buy. The amount is simply the tank’s inside floor area multiplied by the depth, but gravel is sold by the kilogram and aquasoil by the litre, so you also need to know how much each type weighs. This article covers the formula, the right depth for each type, a chart of amounts and bags for standard tank sizes, and what to check before you buy.
Substrate amount = inside width × depth × thickness ÷ 1000
The amount of substrate is the tank’s inside floor area multiplied by how thick you want the layer. Calculate in cm and divide by 1000 to get litres. For a standard 60 cm tank (inside 59 × 29 cm) with a 4 cm layer, that’s 59 × 29 × 4 ÷ 1000 = about 6.8 L.
For substrates sold by weight, such as Oiso gravel or fine river sand, multiply by the weight per litre (bulk density) to convert to kg. Oiso gravel weighs about 1.6 kg per litre, so 6.8 L × 1.6 = about 11 kg. Aquasoil is usually sold by the litre, so just divide the litres by the bag size.
| Substrate | Weight per litre | Common bag | Gaps between grains (share filled by water) |
|---|---|---|---|
| Oiso gravel | About 1.6 kg | 5 kg | About 40% |
| Fine river sand | About 1.5 kg | 2 kg | About 38% |
| Silica sand and other fine sand | About 1.45 kg | 5 kg | About 40% |
| Coral sand | About 1.3 kg | 5 kg | About 45% |
| Aquasoil | About 1.0 kg | 9 L (also 3 L, 8 L and others) | About 50% |
Weight varies by 10–20% depending on grain size and how dry it is. Rather than aiming for the exact amount, it’s safer to get a little more than you calculated and keep the rest for topping up after water changes.
The right depth depends on the substrate and what you keep
Thicker isn’t always better. Too thin and plants can’t root; too thick and water doesn’t circulate at the bottom, so it tends to stagnate. These are commonly used guides.
| Use | Substrate | Depth guide |
|---|---|---|
| Fish only (easy cleaning) | Oiso gravel, gravel | 2–3 cm |
| Fish and hardy plants | Oiso gravel | 4–5 cm |
| Growing plants seriously | Aquasoil | 5–8 cm (thicker at the back) |
| Fish that burrow, such as corydoras and loaches | Fine river sand, fine sand | 2–3 cm |
| Marine fish, African cichlids | Coral sand | 3–5 cm |
| Fry, treatment tanks, easy cleaning | None (bare-bottom tank) | 0 cm |
Planted tanks often slope the substrate, 3–5 cm at the front and 8–10 cm at the back, to create a sense of depth. When sloping, calculate with the average of the front and back depths to get close to what you need. 4 cm at the front and 8 cm at the back averages 6 cm.
Chart of amounts and bags by tank size
These amounts are calculated from the inside dimensions of standard Japanese tank sizes. Bag counts assume 5 kg bags of Oiso gravel, 2 kg bags of fine river sand and 9 L bags of soil (rounded up).
| Tank | Per 1 cm | Gravel 3 cm | Gravel 4 cm | Gravel 5 cm | River sand 3 cm | Soil 5 cm | Soil 8 cm |
|---|---|---|---|---|---|---|---|
| 30 cm standard | 0.53 L | 2.5 kg (1 bag) | 3.4 kg (1 bag) | 4.2 kg (1 bag) | 2.4 kg (2 bags) | 2.6 L (1 bag) | 4.2 L (1 bag) |
| 30 cm cube | 0.84 L | 4.0 kg (1 bag) | 5.4 kg (2 bags) | 6.7 kg (2 bags) | 3.8 kg (2 bags) | 4.2 L (1 bag) | 6.7 L (1 bag) |
| 45 cm standard | 1.01 L | 4.9 kg (1 bag) | 6.5 kg (2 bags) | 8.1 kg (2 bags) | 4.6 kg (3 bags) | 5.1 L (1 bag) | 8.1 L (1 bag) |
| 60 cm standard | 1.71 L | 8.2 kg (2 bags) | 11.0 kg (3 bags) | 13.7 kg (3 bags) | 7.7 kg (4 bags) | 8.6 L (1 bag) | 13.7 L (2 bags) |
| 60 cm wide | 2.58 L | 12.4 kg (3 bags) | 16.5 kg (4 bags) | 20.6 kg (5 bags) | 11.6 kg (6 bags) | 12.9 L (2 bags) | 20.6 L (3 bags) |
| 90 cm standard | 3.84 L | 18.4 kg (4 bags) | 24.6 kg (5 bags) | 30.7 kg (7 bags) | 17.3 kg (9 bags) | 19.2 L (3 bags) | 30.7 L (4 bags) |
| 120 cm standard | 5.07 L | 24.4 kg (5 bags) | 32.5 kg (7 bags) | 40.6 kg (9 bags) | 22.8 kg (12 bags) | 25.4 L (3 bags) | 40.6 L (5 bags) |
Remember the “per 1 cm” column and you can quickly work out any other depth. A standard 60 cm tank needs about 1.7 L per 1 cm, so 6 cm of soil is about 10.3 L, and 2 cm of Oiso gravel is about 3.4 L × 1.6 = about 5.5 kg.
11 kg of Oiso gravel at 4 cm in a standard 60 cm tank is more than two 5 kg bags, so you need three. When the bag count is right on a boundary, decide in advance whether to lay it a little thinner or buy an extra bag, and you won’t be left wondering in the shop.
What to check before buying and laying it
- Rinse Oiso gravel and river sand until the water runs clear before laying. Don’t rinse aquasoil, as it breaks down; put it in as it is
- Aquasoil grains break down over time and often need replacing after about 1–2 years. Oiso gravel can be used indefinitely if you wash it
- With an undergravel filter, lay at least 3 cm over the plate or the filtration won’t work properly
- The substrate’s weight is added directly to the tank’s total weight. 4 cm of Oiso gravel in a standard 60 cm tank adds about 11 kg
- If you mix sands with different grain sizes, the fine grains gradually sink and the layers separate
Substrate grains also take up water volume. A standard 60 cm tank with 4 cm of Oiso gravel holds about 4.1 L less water. How much difference that makes when dosing medicine or salt is covered in your tank’s real water volume, and the weight including substrate in aquarium weight and floor load capacity.
FAQ
- How many kg of gravel does a 60 cm tank need?
- A standard 60 cm tank (inside 59 × 29 cm) needs about 11 kg of Oiso gravel for a 4 cm layer, which is 3 bags of 5 kg. As a guide, 3 cm takes about 8.2 kg (2 bags) and 5 cm about 13.7 kg (3 bags).
- How many litres of aquasoil does a 60 cm tank need?
- A standard 60 cm tank needs about 8.6 L for a 5 cm layer and about 13.7 L for 8 cm. With 9 L bags, that’s 1 bag for 5 cm and 2 bags for 8 cm. If the front and back are different depths, calculate with the average depth.
- How deep should aquarium substrate be?
- As a guide, 2–3 cm for fish only, 4–5 cm if you also plant hardy plants in Oiso gravel, and 5–8 cm for growing plants in aquasoil. For burrowing fish such as corydoras, lay about 2–3 cm of fine river sand.
- How many kg of substrate does a 45 cm tank need?
- A standard 45 cm tank (inside 44 × 23 cm) needs about 4.9 kg of Oiso gravel at 3 cm and about 6.5 kg at 4 cm. With 5 kg bags, that’s 1 bag for 3 cm and 2 bags for 4 cm.
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