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Aquarium Substrate Volume Calculator

Work out how many litres of gravel or sand you need for a layer of a chosen depth.

✔ Vet reviewed · 18 Oct 2026Updated 18 Oct 2026Sources: Pure arithmetic / unit conversion on user inputs
Aquarium Substrate Volume CalculatorFree · instant
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Quick answer A tank 100 cm long and 40 cm wide with a 5 cm layer of substrate needs 20 litres (100 × 40 × 5 ÷ 1,000), about 5.3 US gallons. Enter your tank's length and width and the depth you want to see how much to buy.

How to use the aquarium substrate volume calculator

  1. Enter the inside length and width of the tank.
  2. Enter the depth of substrate you want.
  3. Press Calculate.

Worked example

A tank 100 cm long and 40 cm wide with a 5 cm layer of substrate.

Tank length
100 cm
Tank width
40 cm
Substrate depth
5 cm
20 L (5.3 US gal)
Litres
20 L
US gallons
5.3 gal

Check the pack for weight per litre: gravel, sand and soil differ. Buy a little extra.

Example values are illustrative; this result is produced by the same calculator above.

How we calculate it

litres = length × width × depth (cm) ÷ 1000; US gallons = litres ÷ 3.785411784

Sources: Pure arithmetic / unit conversion on user inputs (no external constant)

Understanding your result

Substrate volume is the length times the width times the depth of the layer. A tank 100 cm long and 40 cm wide with a 5 cm layer needs 100 × 40 × 5 ÷ 1,000 = 20 litres, about 5.3 US gallons.

Use the inside measurements of the tank and the depth you want. A layer is often deeper at the back for planting, so allow for that.

Gravel, sand and plant soil have different densities, so check the pack for weight per litre if you buy by weight. Buy a little extra to allow for waste and sloping.

Common mistakes

  • Using the outside measurements of the tank.
  • Forgetting to rinse the substrate, which loses some volume.
  • Buying exactly the calculated amount with no spare.
  • Mixing units of length and depth.
  • Confusing litres with kilograms.

Good to know

  • Heavy substrate adds weight; check the tank's and stand's rating.
  • Use the Aquarium Water Weight Calculator for the water.
  • Deeper substrate needs more care to keep clean.

Frequently asked questions

How deep should the substrate be?

That depends on your plants and fish. This calculator works out the volume for the depth you choose.

How do I convert litres to kilograms?

It depends on the material because gravel, sand and soil have different densities. Check the pack for weight per litre.

Should I allow extra?

A little extra covers sloping and waste. Buy slightly more than the calculation.

Can I convert litres to kilograms?

Only with the material's density, which varies. Check the pack for weight per litre.

How much extra should I buy?

A little extra covers sloping and loss when rinsing.

Does it work for a planted tank?

Yes. Enter the depth you want, and allow more for a sloped layer.

Reviewed by a licensed veterinarian
Last reviewed 18 Oct 2026 · How we review

Sources

  1. Pure arithmetic / unit conversion on user inputs (no external constant)
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Estimates only. Every pet is different — confirm with your veterinarian.