Aquarium Gravel Calculator

Densities here are the site's standard dry, loose figures — gravel at about 105 lb/ft³, pea gravel 110, sand 100. Branded aquarium gravels vary a little by grain size and rock type, and a bed sloped for planting averages deeper at the back than the front; enter the average depth. Rinse any substrate before it goes in the tank — the dust is harmless to the math but clouds the water for days.

Last updated: 7 November 2026 · Report an error

A gravel bed is just a thin box: length × width × depth. In inches that gives cubic inches; divide by 1,728 for cubic feet, then multiply by the substrate's density to get weight:

Weight (lb) = (L × W × D in³ ÷ 1,728) × density (lb/ft³)

Worked example: a 55 gallon tank measures 48 × 13 in inside. At a 2-inch bed: 48 × 13 × 2 = 1,248 in³ = 0.72 ft³, and at gravel's 104.9 lb/ft³ that is 75.75 lb ≈ 34.4 kg — four 20 lb bags, with a little left over for topping up after the first vacuum. Going to a 3-inch planted bed takes the same tank to 113.6 lb, which is why depth, not tank size, is the decision that moves the bill.

Standard tanks at a standard 2-inch gravel bed. Note the 55 gallon: it needs less gravel than the 40 breeder, because its footprint is narrower — the clearest proof that footprint, not gallons, drives the answer.

About the "1 pound per gallon" rule: it survives because it roughly works at a shallow 1-inch bed on standard footprints (a 10 gallon at 1 inch needs 12.14 lb — close to its gallon count). At the 2-inch depth most tanks actually run, it underestimates by half. Use it for a sanity check, not a shopping list.

Standard aquarium gravel (⅛–¼ in, rounded) is the default for a reason: waste sits on top instead of sinking out of reach, a gravel vacuum cleans it easily, and beneficial bacteria get plenty of surface. Look for inert stone unless you are deliberately buffering — crushed coral and some landscape gravels raise pH and hardness, which suits African cichlids and is wrong for most community tanks.

Pea gravel has a larger grain (around ⅜ in): striking in larger tanks, but food falls into the gaps where small fish can't reach it and it rots — vacuum it diligently, or keep it to tanks with larger, messier fish where the coarse bed is easier to clean than fine gravel would be.

Sand is the kind choice for bottom-dwellers: corydoras, kuhli loaches, and stingrays sift it and rest on it, and sharp gravel can wear barbels down. Plant roots also grip it well. The trade-offs are housekeeping (waste stays visible on top, and sand must be stirred or kept shallow to avoid compacted pockets) and filter intakes, which need a sponge pre-filter near a sand bed. Sand runs slightly lighter than gravel — about 100 lb/ft³ against 105 — so a sand bed for the 55 gallon above weighs 72.2 lb rather than 75.75.

Depth discipline matters more than the choice: 1.5–2 inches for fish-only, 2–3 inches sloped for planted tanks, and think twice before any fine bed passes 3 inches — deep, undisturbed fine substrate can harbour anaerobic pockets whose gas is harmful when disturbed. Depth is also displacement: every inch of bed in a 55 gallon takes roughly 2.7 gallons of swimming and dosing volume.