Inputs used
- Tank length (cm)
- Tank width (cm)
- Front or flat substrate depth (cm)
- Back substrate depth (cm)
- Substrate density (kg/L)
- Bag label unit
- Bag size (number on label)
aquarium substrate calculator
How the Aquarium Substrate Calculator works
Assumptions, formula, inputs, and practical limits for the Aquarium Substrate Calculator.
How this estimate works
The calculator turns tank footprint and desired depth into volume, converts that volume to weight using substrate density, then rounds bag count up. It is a buying estimate, not a livestock-care decision tool, so substrate suitability should still be checked separately.
- Average depth = (front depth + back depth) divided by 2 for a simple straight slope.
- Volume in litres = length x width x average depth in cm divided by 1000.
- Estimated kg = purchase litres x selected substrate density.
- Bag count uses the selected label unit, includes a 10% setup allowance, and rounds up.
Outputs generated
- litres of substrate
- kg/lb required
- bag count
- depth guidance
Worked example
A 90 x 45 cm tank with 5 cm of substrate needs about 20.3 litres. At 1.4 kg/L with a small allowance, that is about 31.2 kg, so four 9 kg bags.
Substrate depth examples
Depth depends on layout, livestock, plants, and the substrate type. These examples are planning ranges, not species guidance.
| Tank footprint | Depth | Approximate volume |
|---|---|---|
| 45 x 30 cm | 3 cm | 4.1 litres |
| 60 x 30 cm | 3 cm | 5.4 litres |
| 60 x 30 cm | 5 cm | 9 litres |
| 90 x 45 cm | 5 cm | 20.3 litres |
| 90 x 45 cm | 8 cm | 32.4 litres |
| 120 x 45 cm | 6 cm | 32.4 litres |
| 120 x 50 cm | 7 cm | 42 litres |
Before you add substrate
- Decide whether the layout is flat, sloped, or planted before estimating depth.
- Check whether the substrate should be rinsed before use.
- Confirm the bag weight and density for the exact brand.
- Leave enough free space for hardscape, filters, and livestock needs.
- Check whether the bag is sold by kg, litres, or both before comparing products.
- Keep plant-root areas, decorative foregrounds, and deep back slopes separate when estimating.
- Account for displacement from large rocks, wood, caves, and filter hardware.
- Keep species-specific substrate requirements separate from the volume estimate.
When this estimate may be wrong
- Sloped aquascapes and deep planted areas can use more substrate than a flat average depth.
- Rocks, wood, and decor displace substrate and water volume.
- Some livestock need specific substrate types or depths that a volume calculator cannot decide.
- Bag count changes when a product is sold by litres instead of kg.
- Wet, rinsed, or porous substrates can behave differently from dry planning-density estimates.
- Deep anaerobic pockets, sharp gravel, or unsuitable grain size can be livestock-specific concerns.
Limits of the estimate
Substrate depth depends on livestock, plants, and tank design. Check species-specific requirements.
Check the needs of your livestock and plants, then confirm bag weights, labelled litres, substrate density, rinsing instructions, and setup notes from the brand you plan to use. For sloped aquascapes, compare the flat average estimate with a deeper back-section estimate.