Aquarium Gravel Calculator

Calculate how much substrate your aquarium needs from the tank's internal dimensions and your chosen depth, with optional bag counts from the product's packaging.

Aquarium gravel calculator

Units
Tank

Measure inside the glass, not the outside of the tank.

The depth of substrate you want across the tank floor.

Excluded base areas

Optional. For flat footprints on the tank floor, such as a rock base. Each excluded area is removed through the full substrate depth — it is not an object’s volume.

Product and packagingOptional — for substrate weight or a bag count

Only a figure for this aquarium product. Construction gravel densities are not used.

Where can I find bulk density?

Ask your quarry, landscape supplier, aggregate supplier or delivery company for the product's bulk density, unit weight, or tons-per-cubic-yard figure.

  • Ask for the loose bulk density if you are ordering loose delivered material.
  • Confirm whether the figure is loose delivered, compacted/in-place, or another condition.
  • Confirm whether “tons” means US short tons or metric tonnes.
Packaging information

Result

Your result will appear here

Enter your tank's internal dimensions and substrate depth to see the substrate volume.

How this calculator works

The calculator multiplies the tank's internal floor area by the substrate depth you want.

Substrate volume = (Tank floor area − Excluded base areas) × Substrate depth

Excluded base areas are flat footprints removed through the full substrate depth. They are not the volume of rocks or decorations.

If you enter the product's bulk density, the calculator estimates the substrate weight. For a bag count, enter the bag volume, the bag weight together with the product density, or the coverage the manufacturer states for the product at a given depth. Bags are rounded up to whole bags.

Choosing and measuring substrate

Measure inside the tank

Use the internal length and width — the space inside the glass. Outside measurements include the glass and frame and overstate the floor area.

Depth is your choice

The right substrate depth depends on your plants, fish and the product. This calculator does not recommend one; enter the depth you plan to use.

Product data, not gravel data

Aquarium substrates differ from one another and from construction gravel. Weight and bag counts here use only the bulk density or packaging details of the product you are buying — never a construction-gravel density. A bag's printed weight alone does not give its volume; for a bag count from weight, the calculator also needs the product density.

Rocks and decorations

If a rock or decoration sits flat on the tank floor, you can exclude its footprint. The calculator removes that footprint area through the full substrate depth. It does not calculate the three-dimensional volume of objects.

For a garden or yard area instead, use the Gravel Calculator.

Worked example

Example: 36 in × 18 in tank, 2 in substrate, one 6 in × 4 in rock base

  1. Tank floor: 36 in × 18 in = 648 in² = 4.5 ft²
  2. Excluded base: 6 in × 4 in = 24 in² = 0.1667 ft²
  3. Substrate area: 4.5 − 0.1667 = 4.333 ft²
  4. Volume: 4.333 ft² × 0.1667 ft = 0.722 ft³

Result: 0.722 cubic feet (0.0205 cubic metres). With bags printed as 0.25 cubic feet each, that is 2.89 bags — rounded up to 3 bags.

Frequently asked questions

What if my substrate slopes from back to front?

The calculator uses one depth across the floor. For an even slope, enter the average of the front and back depths.

How many bags do I need?

Enter the volume printed on the bag, the bag weight plus the product’s bulk density, or the manufacturer’s stated coverage for that product. Coverage is only used at the depth the manufacturer states. The calculator rounds up to whole bags and never guesses a bag size.

Can I subtract a large rock?

You can exclude the footprint it covers on the tank floor. That removes the area under it through the full substrate depth; it is not the rock’s own volume.

Sources & methodology

Substrate volume is geometry plus unit conversion. Sources relevant to this page: