- Multiply the length of the tank by the width of the tank – For example 30 inches x 12 inches = 360 inches.
- Divide the answer by 10 – For example 360 inches / 10 = 36.
How deep should the gravel be in a fish tank?
Aquarium gravel depth
Gravel needs to be at least two inches deep to anchor live or artificial plants, or if covering an undergravel filter. Too deep and the tank loses fish swimming height, and it traps a lot of dirt.
How much gravel do I need for a 40 gallon fish tank?
For one inch of gravel, you’ll use one pound per gallon and for two inches of gravel, you’ll use two pounds per gallon. A 40 gallon tank will use two, 20 pound bags for one inch and four, 20 pound bags for two inches.