Aquarium Substrate Calculator — Sand, Gravel & Aqua Soil Pounds
Calculate how many pounds of sand, gravel, or aqua soil your tank needs from length, width, depth, and density. Presets for common tank sizes.
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Full bio →Use the tank's inside footprint (length × front-to-back width), not the height.
Planted tanks suggest 2–3 in of substrate so root-feeding plants have enough depth to anchor.
Pounds needed = (Length × Width in inches × Depth in inches ÷ 1728) × Substrate density (lb/cu ft). Density varies by product — sand and gravel typically run 85–110 lb/cu ft, while aqua soil is notably lighter (often 40–70 lb/cu ft). Check your specific product's bag label and adjust the density field for the most accurate result. Planted tanks wanting a nutrient-rich base layer under a capping layer should treat this as a starting estimate, not a full layered-substrate plan.
Reference Values
Last verified:| Category | Range | What It Means | Status |
|---|---|---|---|
| Planted tank depth ★ | 2–3 inches | Deeper layer gives root-feeding plants (swords, crypts) room to anchor and access nutrients. Many planted setups add a nutrient-rich base layer under a capping layer of sand or gravel. | ★ Best |
| Fish-only tank depth | 1–2 inches | Standard depth for a community tank with no live plants — enough to look natural and host light beneficial bacteria without trapping excess waste. | Good |
| Fish-only minimal depth | 0.5–1 inch | A thin, easy-to-vacuum layer some fish-only keepers prefer for simpler maintenance. Workable but offers little buffering or bacterial surface area. | Okay |
| Bare-bottom | 0 inches | No substrate at all — common in quarantine or breeding tanks for easy cleaning, but not covered by this calculator. | Poor |
| Sand density | 96–100 lb/cu ft | Typical bagged aquarium sand. Pool filter sand and play sand run similar, slightly finer-grained sand can pack denser. | Good |
| Gravel density | 95–100 lb/cu ft | Typical bagged aquarium gravel — similar bulk density to sand despite the larger particle size. | Good |
| Aqua soil density | 40–70 lb/cu ft | Porous, lightweight planted-tank substrate — notably lighter than sand or gravel. Density varies significantly by brand, so check the product's bag label. | Okay |
| General default ★ | 100 lb/cu ft | Reasonable planning default when the exact product density is unknown — adjust once you know your specific substrate's bagged weight. | ★ Best |
Source: Depth and density conventions aggregated from aquarium substrate calculator methodology published by fishstores.org, the aquarium sand bed calculator at topshelfaquatics.com, and aquarium sand/gravel density specifications published by redflint.com. Bagged product weights vary by brand — always confirm against your specific substrate's packaging when precision matters.
Worked Examples
20-Gallon Long, Fish-Only, Sand
- Footprint
- 30in × 12in
- Tank Type
- Fish-only
- Depth
- 1.5 in
- Material
- Sand (100 lb/cu ft)
(30 × 12 × 1.5 ÷ 1728) × 100 = 0.3125 cu ft × 100 = 31.25 lbs.
55-Gallon, Planted, Sand
- Footprint
- 48in × 13in
- Tank Type
- Planted
- Depth
- 3 in
- Material
- Sand (100 lb/cu ft)
(48 × 13 × 3 ÷ 1728) × 100 = 1.0833 cu ft × 100 = 108.33 lbs — the deeper 3in layer suits root-feeding plants.
29-Gallon, Fish-Only, Gravel
- Footprint
- 30in × 12in
- Tank Type
- Fish-only
- Depth
- 1.5 in
- Material
- Gravel (95 lb/cu ft)
(30 × 12 × 1.5 ÷ 1728) × 95 = 0.3125 cu ft × 95 = 29.69 lbs.
40-Gallon Breeder, Planted, Aqua Soil
- Footprint
- 36in × 18in
- Tank Type
- Planted
- Depth
- 2.5 in
- Material
- Aqua soil (55 lb/cu ft)
(36 × 18 × 2.5 ÷ 1728) × 55 = 0.9375 cu ft × 55 = 51.56 lbs — noticeably lighter than the same volume of sand would be (93.75 lbs at 100 lb/cu ft).
10-Gallon, Fish-Only Minimal Layer, Sand
- Footprint
- 20in × 10in
- Tank Type
- Fish-only (minimal)
- Depth
- 1 in
- Material
- Sand (100 lb/cu ft)
(20 × 10 × 1 ÷ 1728) × 100 = 0.1157 cu ft × 100 = 11.57 lbs — a thin, easy-to-vacuum layer near the low end of the fish-only range.
How to Use This Calculator
- 1
Pick a tank size or enter dimensions
Choose a common preset (10, 20-long, 29, 40-breeder, 55, or 75 gallon) or enter your tank's inside footprint — length and width in inches. Use the flat footprint, not the height.
- 2
Choose planted or fish-only
This sets a suggested depth range: 2–3 inches for planted tanks that need room for roots, or 1–2 inches (down to 0.5–1 inch minimal) for fish-only tanks.
- 3
Set depth and substrate density
Adjust the depth field if you want something outside the suggested range. Pick a material preset (sand, gravel, aqua soil) or enter your specific product's density from its bag label.
- 4
Read your result
The calculator shows total pounds and kilograms needed, plus how many 20 lb or 25 lb bags to buy — round up to the next full bag when shopping.
What Each Value Means
- Tank Footprint (square inches)
- The flat floor area of the tank in square inches — length × width — used because substrate sits on the bottom regardless of the tank's height.
- Substrate Depth (inches)
- How thick the substrate layer is, measured in inches from the glass bottom to the top of the substrate.
- Substrate Density (pounds per cubic foot)
- How much a cubic foot of a given substrate material weighs. Sand and gravel run close to each other (95–100 lb/cu ft); aqua soil is notably lighter (roughly 40–70 lb/cu ft) because it's a porous, baked material.