Soil calculator
Aquarium soil substrate calculator
Nutrient soils are porous and unusually light, so a single bag covers far more floor area than a bag of gravel. Get the weight right before you commit to a planted layout.
Substrate calculator
How much aquarium soil do I need?
Calculated at 40 lb per cubic foot — typical for lightweight planted-tank soil granules.
Result
of aquarium gravel needed
- Metric weight
- 0 kg
- Volume
- 0 in³
- Water volume
- 0 L
- Bags to buy
- 0
Guide
Why soil weighs so much less
Aquarium soil is fired clay or volcanic granule, full of tiny pockets of air. Those pockets are what make it so light: roughly 40 pounds per cubic foot against gravel's 100. In a 40 gallon breeder with a 36 × 18 inch floor, a two and a half inch bed needs about 30 pounds of soil — the same depth in gravel would be closer to 75 pounds.
That difference is the whole reason an aquarium soil substrate calculatorexists. Buy by gravel intuition and you will over-purchase by more than double; buy by bag count alone and you may find one bag barely covers half the floor.
How deep should aquarium soil be?
Two to three inches is the working range for most planted tanks, rising to four at the back where the deep-rooting stems sit. Below two inches the granules compress quickly and root tabs become necessary; much above four inches wastes material in the front half of the tank where nothing is planted. Many keepers lay 1.5 inches of soil and cap it with an inch of fine sand or gravel — the cap holds the nutrients down, stops the water clouding, and gives a cleaner surface to gravel-vac.
Soil is not a permanent bed
Nutrient soils exhaust themselves over twelve to eighteen months as they break down, which is worth knowing before you plan a layout around them. Budget for a full replacement rather than a top-up, because mixing fresh granules into a collapsed old layer gives an uneven floor. When you do replace it, work out the volume first so you order enough in one delivery.
If you are deciding between soil and an inert option, run the same dimensions through the gravel calculator and thesand calculator to see the weight and cost difference side by side, or open the fullaquarium substrate calculator to compare all four materials at once.