Aquarium Forge

Aquarium Substrate Calculator

Enter your tank's footprint and desired substrate depth to get the volume you need —with estimated weight for gravel, sand, and planted tank soil.

Fill in the fields above to calculate.

How It Works

Substrate volume is simply the area of your tank's bottom times the depth you want: Length × Width × Desired Depth. The calculator works in metric internally and reports both liters and cubic inches. To estimate weight, the volume is multiplied by the bulk density of the material you select. Densities differ significantly between gravel, sand, and aquasoil, so the material choice matters as much as the volume.

Formula

Substrate Volume = Length × Width × Desired Depth

Estimated Weight = Volume × Material Density

Example

A 90 × 45 cm tank with 5 cm of sand: 90 × 45 × 5 = 20,250 cm³ = 20.25 liters. At sand's typical density of 1.6 kg/L, that is about 32.4 kg (71.4 lb) of sand.

Important Limitations

  • Weight is an estimate —actual density varies by brand, grain size, and moisture.
  • Results assume a flat substrate bed; sloped or terraced layouts use more material.
  • Bag sizes vary by manufacturer —buy the next size up if you are between bag sizes.

FAQ

How much substrate do I need for my aquarium?

Multiply your tank's length by width by desired depth. A 36 × 12 inch tank with 2 inches of substrate needs about 864 cubic inches (roughly 14 liters), which is around 23 kg of gravel.

How deep should aquarium substrate be?

For most community tanks, 1— inches (2.5— cm) is enough. Planted tanks with root-feeding plants need 2— inches or more so roots can anchor and access nutrients.

How many pounds of gravel do I need per gallon?

A common rule of thumb is 1—.5 pounds of gravel per gallon of tank volume, but that ignores tank footprint. Calculating by length × width × depth is far more accurate.

Is substrate weight exact?

No. Bulk density varies by brand, grain size, and moisture content. The calculator uses typical density ranges (gravel ≈1.68 kg/L, sand ≈1.6 kg/L, aquasoil ≈0.75 kg/L), so treat the weight as a planning estimate.

What is the difference between gravel, sand, and aquasoil?

Gravel is inert and easy to clean. Sand is finer and compacts more, suited to fish that dig. Aquasoil buffers water chemistry and holds nutrients for plants, but it is lighter and breaks down over several years.

Sources

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