Gravel Calculators

Aquarium Gravel Calculator

How much substrate does your tank actually need? Pick a standard tank size or enter your tank's footprint, choose a depth, and get the answer in pounds and kilograms — the units substrate is sold in, not tons and cubic yards.

Step 1 · Your tank

Measure the inside bottom of the tank — length × width of the floor, not the tank height.

Step 2 · Substrate depth

1–2" for fish-only tanks; 2–3" if you're growing live plants.

Step 3 · Substrate type

Sand packs tighter than gravel — the same depth weighs more and isn't a 1:1 swap.

Substrate weight by tank size

Standard aquarium gravel at common depths — for quick shopping without the calculator.

Pounds of standard aquarium gravel by tank and depth
Tank Footprint 1" deep 2" deep 3" deep
10 gallon20 × 10 in12 lb24 lb36 lb
20 gallon long30 × 12 in22 lb44 lb66 lb
29 gallon30 × 12 in22 lb44 lb66 lb
40 gallon breeder36 × 18 in39 lb79 lb118 lb
55 gallon48 × 13 in38 lb76 lb114 lb

The old "one pound per gallon" rule approximates a shallow bed and ignores footprint — two very different tanks of the same gallonage can need quite different substrate amounts. Your tank's actual floor dimensions are what matter.

Practical substrate notes

  • Rinse before use. New gravel and sand carry dust that will cloud a tank for days. Rinse in batches until the water runs mostly clear.
  • Depth affects plants. Live plants root best in 2–3 inches; fish-only tanks are easier to vacuum at 1–2 inches. Sloping deeper at the back looks natural and gives plants room where they need it.
  • Very deep fine beds can compact and go anaerobic (smelly pockets). If you want a deep sand bed, research it as its own approach rather than just pouring more in.
  • Decorative "pea gravel" from a hardware store can work in tanks if it's washed and inert, but verify it won't alter pH — aquarium-specific substrate is tested for that. Landscape pea gravel quantities for outdoor projects live on the pea gravel calculator instead.

Gravel Calculator

Yards and tons for outdoor projects — patios, driveways, paths.

Pea Gravel Calculator

Walkways, beds, and play areas at pea gravel depths.

Gravel Types and Sizes Guide

Material differences between gravel, crushed stone, and sand.

Aquarium substrate FAQ

How much gravel do I need for a 20 gallon tank?

A 20 gallon long tank (30 × 12 in) at a typical 2-inch depth needs about 44 pounds of standard aquarium gravel; at 3 inches, about 66 pounds. The old rule of thumb of 1 pound per gallon lands near a 1-inch bed in standard tanks, but the calculator above uses your actual footprint and depth, which is more accurate.

How deep should aquarium substrate be?

1–2 inches suits fish-only tanks and easy cleaning. Planted tanks generally want 2–3 inches so roots can establish, often sloped higher at the back. Very deep beds (4 inches plus) of fine substrate risk compacting and going anaerobic, so depth should be deliberate, not accidental.

Should I use sand or gravel in my aquarium?

Both work, but they're not interchangeable by volume: sand packs tighter, so a given depth of sand weighs more and displaces less water than the same depth of gravel. Sand suits bottom-dwelling fish and planted tanks; gravel is easier to vacuum and allows more water flow. The calculator shows weights per material so you can compare honestly.

Do I need to rinse aquarium gravel before use?

Yes. New substrate carries dust and fines that will cloud your tank for days otherwise. Rinse in batches under running water until the water runs mostly clear — then you still expect slight cloudiness for a few hours after filling.