How Much Substrate?

ARTICLE by SS, November 08, 2015

Take the guesswork out of planning your substrate bed by calculating how much you'll need for your project. This article will show you walk you through calculations for common aquarium shapes. You may need a calculator and ruler! If you need help figuring out your substrate needs, contact us! We're happy to assist.

The choice of substrate for freshwater aquariums generally boils down to aesthetic preference. Rather than get into what color matches what plant, animal, or whatever, we're going to assume that you have an idea for your design. This will allow us to skip straight to the big question: How do I figure out how much substrate I need?

To start, let's talk about volume, the amount of space something occupies. For most of our substrates, our standard 2-3 pound bags have a volume of about 50in³. When available, we try to provide substrate volume on each item page, so keep an eye out.

Where to find volume on

With this information in hand, you just need to figure out the volume of substrate you need for your aquarium and you're pretty much done!

We've broken this article down by common aquarium shapes - select the one that most closely matches your aquarium and we'll help you figure out the approximate volume you need.

Once you've determined the volume of substrate you'll need. Divide that by the approximate volume we provide you for our substrates.


450in³ (volume needed) ÷ 50in³ (volume of 3lb bag) = 9 bags needed

Rectangular Aquarium


Figuring out of volume you need for a flat substrate bed is the most straightforward.


Volume Needed = L x W x H
L = Length
W = Width
H = Desired Height
Aquarium Diagram - Level Rectangular


Calculating the volume of a sloped substrate bed in a rectangular shaped aquarium requires Length, Width and two height measurements: Front Height and Back Height.


Volume Needed = L x W x (H₁ + H₂) x 0.5
L = Length
W = Width
H₁ = Desired Height (front)
H₂ = Desired Height (back)
Aquarium Diagram - Sloped Rectangular

Hex Aquarium

Calculating the volume of a level substrate bed in a six-sided hex aquarium requires four measurements.


Volume Needed = (L₁ + L₂) x W x H x 0.5
L₁ = Length (corner to corner)
L₂ = Length (front glass panel)
W = Width
H = Desired Height
Aquarium Diagram - Level Hex

Cylinder Aquarium

Calculating the volume of a level substrate bed in a cylindrical aquarium requires two measurements.


Volume Needed = π x R² x H
π = 3.142
R = Radius (half the length)
H = Desired Height
Aquarium Diagram - Level Cylinder

Small or Irregular Container

For small, irregularly shaped aquariums or containers, it's often easier to measure volume in cups of water. Each cup of water is roughly equivalent to 0.75 pounds of sand or gravel. Lava substrate is lighter in weight and can be estimated at 0.40 pounds per cup.

Add water into your container to the height you'd like your substrate to go (be sure to keep track of how many cups of water you are adding). Multiply the number of cups of water you get by the equivalent number of pounds per cup and you're done.

Aquarium Diagram - Small Containers
Pouring water from irregular container

0.75 pound/cup x 2 cups = 1.5 pounds needed