Aquarium Gravel Calculator: Substrate and Bags

Aquarium Gravel Calculator

Estimate substrate volume, weight, whole bags and cost for a uniform or sloped aquarium bed.

Units

Tank footprint

Number of identical tanks

Inside length (in)

Inside width (in)

Inside diameter (in)

Known bottom area (in²)

Front depth (in)

Back depth (in)Use the same depth twice for a level bed.

Substrate exampleExamples only; edit density or label coverage below.

Product, bags and allowance

Bag calculation basis

Area intentionally left bare (%)

Contouring / handling allowance (%)

Bulk density (lb/ft³)Editable planning value; use the product specification when available.

Coverage per bag (in²)

Coverage depth (in)

Bag weight (lb)

Price per bag (optional)

Substrate to plan for—

—Planned substrate volume

—Estimated required weight

—Whole bags to buy

—Covered bottom area

—Estimated purchased excess

—Bag cost

Depth comparison

Average depth	Planned volume	Estimated bags

Formula

For a rectangular aquarium, bottom area = inside length × inside width. For a round tank, area = π × diameter² ÷ 4. A straight front-to-back slope uses average depth = (front depth + back depth) ÷ 2. Substrate volume equals covered bottom area × average depth × number of tanks, then the selected allowance is added.

Why product coverage can be more reliable

Bulk density changes with grain size, porosity, moisture and compaction. If the bag states how much area it covers at a stated depth, choose manufacturer coverage. The calculator converts that claim into volume per bag and rounds the purchase up to whole bags. Otherwise, it multiplies planned volume by the editable bulk density.

Worked example

A 30 × 12 in bottom with a bed sloping from 2 to 3 in has an average depth of 2.5 in. Its raw volume is 900 in³, or about 14.75 L. Adding 5% for contouring and handling gives about 15.49 L before whole-bag rounding.

Limits

Use inside bottom dimensions, not the outside glass dimensions or advertised tank capacity.
The slope calculation assumes depth changes evenly from front to back.
“Bare area” means bottom area that will intentionally receive no substrate; rocks placed on top do not automatically justify subtracting their full footprint.
Density presets are editable examples, not product specifications. Granule shape, compaction and moisture can change actual weight.
Confirm that the stand, tank and floor can support the final filled system; this calculator estimates substrate only.

Related tools: the Gravel Calculator estimates landscaping aggregate, while the Volume Calculator handles general geometric volumes.