Gravel in a fish tank looks great, but determining how much gravel to buy can be confusing. Most aquarium enthusiasts recommend a coverage depth of 2 inches. Too much gravel can lead to unsanitary conditions because food can become trapped deep below the surface of the gravel where your fish cannot reach it. Also, gravel takes a long time to clean because it either has to be removed from the tank and rinsed completely, or regularly cleaned with a gravel vacuum.
Measure the length of your fish tank in inches.
Measure the width of your fish tank in inches.
Multiply the length times the width.
Divide that number by 10. Your result is roughly how many pounds of gravel you will need to buy in order to cover the bottom of your tank with an average of 2 inches of gravel (the recommended level).
To increase or decrease the depth, multiply your result by whatever percentage increase or decrease you would like. For example, a depth of 3 inches would require 150 per cent of the gravel that 2 inches requires. Multiply your result by 1.5 and you will have the amount of pounds of gravel you need to fill your tank. Four inches would be 200 per cent, so multiply your result by 2, and so on.
If you are buying a special form of substrate (such as silica) that is finer than typical fish tank gravel, you will need to buy more to compensate for its greater density. Conversely, if you buy a less dense substrate, such as crushed coral, you should buy fewer pounds of it.