Flat and sloped bed formulas
For a flat bed, multiply internal length, width, and depth in centimeters, then divide by 1,000 for liters. For a slope, use the average of front and back depth.
Use internal dimensions rather than the outside glass size.
- Flat liters = length × width × depth ÷ 1,000
- Sloped liters = length × width × average depth ÷ 1,000
Example for a 60 cm aquarium
A 60 × 30 cm floor sloping from 3 cm to 8 cm has an average depth of 5.5 cm and a base volume of 9.9 L.
Adding a 10% margin gives about 10.9 L, and bag count rounds up to the product's package size.
Why liters and kilograms differ
Soil, sand, and gravel have different bulk densities. Use the package's volume, weight, or density instead of assuming one liter equals one kilogram.
Wet and dry material also differ, and stand loading should include glass, water, rocks, and equipment separately.
Layouts with rocks and structures
Large rocks, wood, and undergravel structures are not automatically subtracted. Reduce the estimate when they occupy a meaningful part of the base.
Rounding up prevents shortages, so some unused material is normal.
Measure the internal footprint and target depth
Use internal length and width rather than outside dimensions. Exclude filter chambers, silicone, and structures that occupy the bottom. For a straight slope, approximate volume with the average of front and back depths.
A 60×30 cm interior with 3 cm at the front and 7 cm at the back has a 5 cm average and roughly 9 L theoretical volume. Divide complex terraces and hardscape into separate regions and add them. A uniform-depth result is a purchasing baseline.
- Use internal length and width
- Approximate a straight slope with average depth
- Calculate complex regions separately
Convert litres to weight and bags
Volume in litres is length × width × average depth ÷ 1,000. For litre-labelled bags, add an explicit allowance and round bags up. For kilogram products, use the manufacturer's product-specific density; equal litres of soil, sand, and gravel do not weigh the same.
If the estimate is 9 L and bags are 3 L, the theoretical need is three bags. A 5–10% allowance can cover shaping and loss, but excess active soil may be wasteful. If a product chart differs, inspect its assumed tank dimensions and depth.
- Litres = length × width × average depth ÷ 1,000
- Use product density for kilogram conversion
- Round bag count up and label the allowance
Interpret depth for soil, sand, and gravel
Materials settle differently because of grain size and compaction. Slopes can flatten after filling, so do not assume substrate alone will hold a tall layout without terraces or structure.
Very deep beds may complicate maintenance for some livestock and filtration approaches, while digging animals can reshape them. The calculator estimates quantity; product safety and suitability depend on livestock, plants, cleaning method, and instructions.
- Allow for material-specific settling
- Plan support for steep layouts
- Match depth to livestock, plants, and maintenance
Correct the estimate after setup
Record theoretical litres, allowance, purchased bags, actual bags used, and final depth. That creates a personal conversion for future tanks and top-ups. Rinsing can remove fines, and mixing old and new substrate makes new-product depth harder to measure.
If material is short, recheck depth, internal dimensions, excluded hardscape area, and package units. Store leftovers under the manufacturer's directions. For stand loading, add water, glass, rock, equipment, and substrate rather than considering substrate alone.
When planted and decorative areas use different depths, calculate regions separately. Mark dimensions on a sketch, add regional volumes, and then include only a modest allowance for material mixing at boundaries.
- Separate theoretical, allowed, and purchased quantities
- Record actual use and final depth
- Include all tank components in load planning