Substrate calculator
Find out exactly how many bags of aquasoil, sand or gravel your tank needs — for any shape, depth and brand. Supports flat and sloped layouts with accurate bag counts and leftover.
How much substrate depth do you actually need?
The standard recommendation for planted tanks is 6–8 cm average depth. This gives roots enough soil to anchor firmly, access stored nutrients, and grow without restrictions. It also provides enough mass to maintain stable chemistry — aquasoils that are too shallow can be exhausted more quickly by plant roots, and the buffering capacity is proportional to volume.
Foreground carpeting plants such as Hemianthus callitrichoides (HC Cuba) and Eleocharis parvula need at least 5 cm of substrate for adequate rooting. Background plants with larger root systems — Vallisneria, Echinodorus, large Cryptocorynes — benefit from 8–10 cm, particularly at the back of the tank where they are planted. This is one reason a sloped substrate makes practical sense, not just aesthetic sense.
Depths above 10–12 cm risk creating anaerobic pockets in the deepest layers. Without adequate water flow and plant root activity, organic matter decomposes anaerobically, producing hydrogen sulphide — toxic to fish and invertebrates. If you want very deep substrate for specific plants, a coarser base layer under the active substrate helps water circulation at depth.
Sloped substrate: the Nature Aquarium approach
The front-to-back slope is a defining feature of the Nature Aquarium aesthetic developed by Takashi Amano. Substrate rises from 3–4 cm at the front glass to 8–10 cm at the back. The technique serves three purposes simultaneously: it creates visual depth by tilting the substrate plane toward the viewer, it gives background plants a deeper root zone without wasting aquasoil in foreground areas, and it provides a natural-looking terrain profile that mirrors riverbeds and lake margins.
In iwagumi compositions, the slope also works with stone placement — rocks are partially buried in the deeper rear substrate, creating a more naturalistic embedded look than rocks simply sitting on a flat bed. The calculator supports sloped layouts with separate front and back depth inputs, giving you an accurate total volume and bag count for this style.
Sloped layout bag count
The calculator averages front and back depths to estimate the total substrate volume needed for a sloped layout. In practice, substrate will settle and shift slightly after filling — buy one extra bag as a buffer if your counts come out near a whole number.
Why bag counts vary so much between substrates
Aquasoils and sands are sold by volume (litres) or by weight (kilograms), but neither tells you directly how much tank footprint they cover at a given depth. The critical figure is bulk density — the mass of the material per litre of volume as it sits loosely packed. Aquasoils have a bulk density of roughly 0.65–0.72 kg/L. Fine sand typically runs 1.4–1.6 kg/L.
This means a 9-litre bag of ADA Amazonia covers the same footprint depth as a 9-litre bag of sand — but they weigh very different amounts. Aquasoil is sold by volume, so the bag size tells you directly how many litres it contains. Sand sold by weight requires a density conversion: a 5 kg bag of fine sand at 1.5 kg/L contains approximately 3.3 litres of material.
The calculator handles all of this automatically — select your substrate, enter your dimensions and depth, and get the exact bag count with leftover calculated. This saves you both over-buying and the frustration of being one bag short mid-scape.
After calculating your substrate, enter the depth into the tank volume calculator to get your accurate net water volume for CO₂ and fertiliser dosing.