Tank footprint to whole bags
Aquarium Substrate Calculator
Estimate how much sand, gravel or aquasoil your tank needs.
Volume is geometric. Weight and bag counts depend on the density and bag weight you provide, so treat them as planning estimates.
How it works
Keep the geometry and the material assumptions separate, so you can see which part of the estimate is certain.
Average the depth
Add front and back depth, then divide by two.
Find the volume
Multiply tank length, width and average depth.
Apply density
Only use a density from the package or your own measurement.
Round bags up
Divide buffered weight by bag weight, then round up to a whole bag.
Worked example: a flat 60 cm tank
A 60 × 30 cm footprint with 5 cm at both the front and back has an average depth of 5 cm and a volume of 9 L. If your material is 1.5 kg/L, a 10% buffer brings the estimate to 14.85 kg. With 5 kg bags, plan for 3 whole bags.
60 × 30 × 5 cm
9 L → 14.9 kg → 3 bagsDensity and bag size are example inputs, not universal substrate values.
Flat vs. sloped substrate
For a flat bed, enter the same depth at the front and back. For a slope, enter the two different depths. A slope can rise or fall toward the back; the calculation uses the average of the two ends either way. Rocks, wood and complex terraces can displace substrate, so the result remains an estimate.
Density and bag labels
If a package gives both volume and net weight, divide weight by volume to estimate bulk density in kg/L or lb/US gal. Grain size, compaction and moisture can change the real value. Never assume sand, gravel and aquasoil share one density, and use the bag's printed net weight for the bag count.
Related aquarium tools
Aquarium substrate FAQ
How much substrate do I need for my aquarium?
Measure the tank's inside length and width, then multiply that footprint by the average substrate depth. This calculator converts the volume and, when you provide a material density, estimates weight.
How do I calculate substrate for a sloped aquascape?
Enter the depth at the front and back of the tank. The calculator uses their average depth, so either a front-to-back rise or fall works.
How deep should aquarium substrate be?
There is no single depth that suits every aquarium. Plant roots, fish behavior, substrate material and the aquascape design all affect the appropriate depth.
Why does substrate weight vary by material?
Grain size, pore space, compaction and moisture change bulk density. Use a manufacturer's stated density or a value measured from your own material instead of assuming all sand, gravel or aquasoil weighs the same.
Should I buy extra substrate?
A planning buffer can cover settling, contours and small measuring differences. The default 10% is adjustable and is not a required purchase amount.