Your results will appear here.
Enter your values and press Calculate.
Multiply tank length by width by gravel depth for cubic inches, then divide by 20 for pounds. A 36 by 18 inch tank with 2 inches of gravel needs 1296 cubic inches, about 64.8 pounds.
Gravel volume in cubic inches equals tank length multiplied by tank width multiplied by gravel depth, all in inches. Gravel weight in pounds equals that volume divided by 20, a planning average for common aquarium gravel. This aquarium gravel calculator therefore works from the tank footprint, not from gallons, because footprint is what actually determines how much substrate covers the bottom. A 36 by 18 inch tank with 2 inches of gravel needs 1,296 cubic inches, about 64.8 pounds.
Enter the inside tank length and width in inches, plus your planned gravel depth in inches. The result is the fish tank gravel amount in volume and weight, the gravel volume in cubic inches and the estimated gravel weight in pounds, ready to convert into bag counts at the shop. Measure inside dimensions, not the outside of the glass, and re-measure after any background or divider is fitted, because both steal footprint.
Two inches of aquarium gravel depth in inches suits most tanks: deep enough to anchor decorations, shallow enough to avoid dead zones where waste collects. A planted tank substrate calculator approach uses 2 to 3 inches, or a 1 inch nutrient layer plus 2 inches of gravel on top, so heavy root feeders like Amazon swords stay anchored. Undergravel filters need at least 2 inches so water pulls through the bed evenly, and tanks over 55 gallons often run 3 to 4 inches. A front-to-back slope, 1 inch at the front rising to 3 inches at the back, creates depth in the view and lets waste roll forward where a siphon can reach it; for a slope, use the average depth in this calculator.
The old rule of 1.5 pounds of gravel per gallon for a standard tank, or 2 pounds per gallon for a planted tank, is a rough shortcut, and it fails when gravel density changes. Weight does not equal volume: heavy river stones, light volcanic aqua soil and sand all weigh differently per cubic inch, so a gallon rule can be off by nearly double for aqua soil. Footprint math avoids that trap, because length multiplied by width multiplied by depth gives the true volume, and only the final density step varies by material. If you buy aqua soil instead of gravel, expect far fewer pounds for the same volume, and check the bag weight rather than trusting a gallon rule.
A 20 gallon tank with a 24 by 12 inch footprint and 2 inches of gravel needs 576 cubic inches, about 28.8 pounds, so two 20 pound bags cover it with a spare for top ups. A 10 gallon tank at 20 by 10 inches and 2 inches needs 400 cubic inches, about 20 pounds. A 55 gallon tank at 48 by 13 inches and 2 inches needs 1,248 cubic inches, about 62.4 pounds. Buy one bag more than the estimate: a spare bag in storage beats stopping halfway through a setup with a bare patch at the back.
Always rinse gravel before adding it, in a bucket until the overflow water runs clear, or the dust will cloud the tank for days. Use only gravel labeled aquarium safe: driveway gravel can contain limestone or oily residues that spike pH and harm fish. For an aquarium sand vs gravel calculator choice, remember sand suits bottom feeders like Corydoras, whose bellies scratch on rough gravel, while gravel is easier to clean with a siphon vacuum. Vacuum about 25 percent of the gravel surface during each weekly water change, never the whole bed at once, so beneficial bacteria survive.
Multiply tank length by width by depth in inches for cubic inches, then divide by 20 for pounds. A 36 by 18 inch tank with 2 inches of gravel needs about 64.8 pounds.
Two inches suits most tanks. Planted tanks often use 2 to 3 inches so roots anchor well, while very deep beds can trap waste and create dead zones.
A typical 20 gallon tank with a 24 by 12 inch footprint and 2 inches of gravel needs about 28.8 pounds by this estimate, or about 30 pounds by the 1.5 pounds per gallon rule.
It depends on your fish. Sand suits Corydoras and loaches, because it will not scratch their bellies, while gravel is easier to clean with a siphon and anchors plants better.
The common shortcut is 1 to 1.5 pounds per gallon for a standard tank and 2 pounds per gallon for a planted tank. Footprint math is more accurate, because it uses your actual tank dimensions instead of a flat gallon constant.
No. Driveway gravel often contains limestone or oily residues that will spike pH and harm fish. Only use gravel labeled aquarium safe, and rinse it before adding it.
Natural quartz gravel will not, but aragonite or crushed coral will raise pH sharply. Check your water with a liquid test kit if you use a calcium-based substrate.
Vacuum about 25 percent of the gravel surface during every weekly water change. Do not clean the whole bed at once, or you will remove too much beneficial bacteria.
Yes, but rinse it thoroughly first and add it a handful at a time, so you do not trap fish or cloud the water. Unless you use an active plant soil that breaks down, gravel itself never needs replacing.