How much substrate do I need? Sand, gravel and aquasoil by tank size

How much sand or gravel you need depends on your tank's floor and how deep you want the bed, not on how many gallons it holds. Find your tank below for pounds of sand and gravel, or litres of aquasoil.

By ScapeMath · Updated November 3, 2026 · Every number on this page is computed with the same formulas as our calculators.

Want the exact figure for your tank? Enter your inside floor size, front and back depth and substrate, and the calculator gives the weight and the number of bags to buy. Open the free substrate calculator.

The formula

Pounds = length (in) × width (in) × depth (in) ÷ 1,728 × bulk density (lb/ft³) Litres = length (cm) × width (cm) × depth (cm) ÷ 1,000; kg = litres × bulk density (kg/L)

Bulk density is the weight of a loose, dry measure. CaribSea publishes 100 lb/ft³ for aragonite and cichlid sands, 90 for Fiji Pink, 85 for Special Grade reef sand, 80 for Eco-Planted / Eco-Complete and 75 for crushed coral. Generic dry sand is about 1,555 kg/m³ (97 lb/ft³) and gravel 1,680 kg/m³ (105 lb/ft³).

Substrate chart for common tanks (pounds)

Pounds for a flat bed over the nominal floor. Measure inside the glass for an exact figure; inside floors are a little smaller, which leaves you a small margin.

Weight of substrate by tank and depth. Aragonite / cichlid sand at 100 lb/ft³; generic gravel at 1,680 kg/m³; Eco-Complete at 80 lb/ft³.
Tank	Floor (in)	Sand, 1 in	Sand, 2 in	Sand, 3 in	Gravel, 2 in	Eco-Complete, 2 in
5.5 gallon	16 × 8	7 lb	15 lb	22 lb	16 lb	12 lb
10 gallon	20 × 10	12 lb	23 lb	35 lb	24 lb	19 lb
20 gallon high	24 × 12	17 lb	33 lb	50 lb	35 lb	27 lb
20 gallon long	30 × 12	21 lb	42 lb	62 lb	44 lb	33 lb
29 gallon	30 × 12	21 lb	42 lb	62 lb	44 lb	33 lb
40 gallon breeder	36 × 18	38 lb	75 lb	113 lb	79 lb	60 lb
55 gallon	48 × 13	36 lb	72 lb	108 lb	76 lb	58 lb
75 gallon	48 × 18	50 lb	100 lb	150 lb	105 lb	80 lb
90 gallon	48 × 18	50 lb	100 lb	150 lb	105 lb	80 lb
120 gallon	48 × 24	67 lb	133 lb	200 lb	140 lb	107 lb
125 gallon	72 × 18	75 lb	150 lb	225 lb	157 lb	120 lb

Substrate chart in litres and kilograms

Bed volume for common metric floors, the weight of a 5 cm bed of generic dry sand, and how many 9 L bags of aquasoil a 5 cm average bed takes with 10% extra.

Bed volume by floor and depth. Sand at 1.555 kg/L.
Floor	3 cm deep	5 cm deep	8 cm deep	Sand, 5 cm	9 L aquasoil bags, 5 cm
45 × 27 cm	3.6 L	6.1 L	9.7 L	9.4 kg	1
60 × 30 cm	5.4 L	9.0 L	14.4 L	14.0 kg	2
60 × 45 cm	8.1 L	13.5 L	21.6 L	21.0 kg	2
75 × 45 cm	10.1 L	16.9 L	27.0 L	26.2 kg	3
90 × 45 cm	12.2 L	20.3 L	32.4 L	31.5 kg	3
120 × 45 cm	16.2 L	27.0 L	43.2 L	42.0 kg	4
120 × 60 cm	21.6 L	36.0 L	57.6 L	56.0 kg	5

Why "1 pound per gallon" doesn't work

CaribSea's rule of thumb is 1–2 lb of substrate per gallon. It works for some tanks and not others, because tall tanks hold more water over the same floor. Here is 1 in of aragonite sand per nominal gallon:

1 in of aragonite sand (100 lb/ft³) per gallon of tank
Tank	1 in of sand	Per gallon
10 gallon	11.6 lb	1.16 lb
20 gallon long	20.8 lb	1.04 lb
29 gallon	20.8 lb	0.72 lb
40 gallon breeder	37.5 lb	0.94 lb
55 gallon	36.1 lb	0.66 lb
75 gallon	50.0 lb	0.67 lb
125 gallon	75.0 lb	0.60 lb

How deep should the bed be?

Planted tanks, aquasoil: about 5 cm (2 in) on average. ADA sizes one 9 L bag of Amazonia for a 60 × 30 cm tank, which is exactly a 5 cm bed. Slope it deeper at the back for taller plants.
Reef, shallow sand bed: 1.5–2 in (4–5 cm), per Marine Depot / Bulk Reef Supply.
Reef, deep sand bed: 6–8 in (15–20 cm) of fine sand.
Coarse sand and gravel: keep it under 2–3 in, because deep coarse beds trap detritus.

Aragonite and crushed coral slowly raise pH and KH, which suits reefs and African cichlids but not soft-water tanks. Check after setup with the KH & GH converter.

Buying tips

Buy about 10% extra for levelling, slopes and spills.
Sand and gravel sell by weight, aquasoil by volume. Compare aquasoil bags in litres, not kilograms.
"Live" sand bags include water, so they cover a little less than their weight suggests.
Rock placed on the glass before the sand takes up some floor, so you need slightly less; rock set on top of the bed changes nothing here, but it adds weight to the stand. See the full-tank weight example in the tank sizes chart.

Gear for this job

Sand or gravel: buy by the weight in the charts.
Look for: A stated grain size and material. Aragonite and crushed coral raise pH and KH, so use them for reef and African cichlid tanks, and inert quartz or similar for soft-water tanks. Sold by weight, so size it with the calculator.
Aquasoil (planted tanks): buy by the litres in the metric chart.
Look for: Sold by volume (litres): check the bag size against the calculator. Read the label on ammonia release in the first weeks, and don't rinse granular soils, which crumble.
Substrate spatula: for shaping and smoothing slopes.
Look for: A flat stainless or plastic blade long enough to reach the back glass, for building and smoothing a slope without scratching.

We choose gear by what the job needs, never by commission. Full gear checklist · Affiliate disclosure

Common questions

How much sand do I need for a 40 gallon breeder?

Its floor is 36 × 18 in, so a 2 in bed is 1,296 in³ (21.2 L). At CaribSea's 100 lb/ft³ for aragonite and cichlid sands that's 75 lb. With 10% extra, buy 5 bags of 20 lb.

How many pounds of gravel for a 10 gallon tank?

A 10 gallon floor is 20 × 10 in. A 2 in bed is 6.6 L, which is 24 lb of generic dry gravel (1,680 kg/m³) or 23 lb of aragonite sand. That's about 2.4 lb per gallon at 2 in.

How much aquasoil do I need for a 120 cm tank?

For a 120 × 45 cm floor at a 5 cm average depth: 120 × 45 × 5 ÷ 1,000 = 27 L, or 4 bags of 9 L with 10% extra. A slope from 3 cm at the front to 8 cm at the back takes 29.7 L, because its average depth is 5.5 cm.

Is it 1 pound of sand per gallon?

Only for some tanks. CaribSea's rule of thumb is 1–2 lb per gallon, but a bed depends on the floor area, not the water. One inch of aragonite sand is 1.04 lb per gallon in a 20 long but 0.66 lb per gallon in a 55, because the 55 is mostly extra height.

How deep should sand be in a reef tank?

Marine Depot (Bulk Reef Supply) describes a shallow sand bed as 1.5–2 in and a deep sand bed as 6–8 in of fine sand, and advises keeping coarse sand under 2–3 in. A 6 in deep bed on a 75 gallon's 48 × 18 in floor is about 270 lb of CaribSea Fiji Pink at its listed 90 lb/ft³.

Does a sloped bed need more substrate?

Only by its average depth. A bed that slopes evenly from 1 in at the front to 3 in at the back takes exactly as much as a flat 2 in bed, because the average of 1 and 3 is 2.

References

The tables on this page are generated from the calculators' own code and checked by automated tests. Last reviewed November 3, 2026. Found an error? Tell us.

Calculators for this job

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