# Aquarium substrate calculator

> Enter the tank footprint and your substrate depth to get the substrate volume in US gallons and the wet weight in pounds. A 24 × 12 in (≈ 61 × 30 cm) tank with a 2 in (≈ 5.1 cm) bed of sand (≈1.5 kg/L) holds 2.49 US gal (≈ 9.4 L) of substrate and weighs 31.2 lb (≈ 14 kg) — the worked example below uses the same shape, so the numbers shown in this intro always match the calculator.

Use the interactive calculator on the page: https://petguidecalc.com/aquarium/substrate-calculator/. Enter the tank length, width, and substrate depth in cm or inches, pick a bulk density that matches your substrate (sand ≈ 1.5 kg/L, gravel ≈ 1.6 kg/L, aquasoil ≈ 0.7 kg/L dry), and the tool returns volume in liters plus weight in kg and pounds.

## How much substrate do I need for my aquarium?

Substrate volume is the tank footprint (length × width) times the depth of the bed; 231 cubic inches make one US gallon. A 24 × 12 in tank with a 2 in bed holds 2.49 US gal (≈ 9.4 L); at sand density (≈1.5 kg/L) that is about 31 lb (≈ 14 kg) of substrate.

## Common substrate amounts at a glance

| Tank footprint | Depth | Volume | Weight |
|---|---|---|---|
| 24 × 12 in (≈ 61 × 30 cm) | 1 in (≈ 2.5 cm) | 1.25 gal (4.72 L) | 15.6 lb (7.08 kg) |
| 24 × 12 in (≈ 61 × 30 cm) | 2 in (≈ 5.1 cm) | 2.49 gal (9.44 L) | 31.2 lb (14.16 kg) |
| 36 × 18 in (≈ 91 × 46 cm) | 2 in (≈ 5.1 cm) | 5.61 gal (21.24 L) | 70.2 lb (31.86 kg) |
| 48 × 18 in (≈ 122 × 46 cm) | 2.75 in (≈ 7 cm) | 10.29 gal (38.94 L) | 128.8 lb (58.40 kg) |

Weights assume sand at ≈1.5 kg/L. Gravel runs heavier (≈1.6 kg/L); aquasoil runs lighter (≈0.7 kg/L dry) and swells when soaked.

## How the substrate volume is calculated

Substrate sits in a rectangular slab under the tank, so the volume is length × width × depth. Worked in inches that yields cubic inches, and 231 in³ = 1 US gal; worked in centimeters, divide by 1,000 to get liters. Either path lands on the same volume the calculator reports.

Weight is volume × bulk density. Sand is roughly 1.5 kg/L wet, gravel 1.6 kg/L, and aquasoil 0.5–0.7 kg/L dry before it swells (it can roughly double its weight when soaked). Pick a density that matches the substrate you are buying — wet weight matters more than the dry bag weight.

Worked example from the calculator: a 24 × 12 in (≈ 61 × 30 cm) tank with a 2 in (≈ 5.1 cm) bed at 1.5 kg/L returns 2.49 US gal (≈ 9.4 L) and 31.2 lb (≈ 14 kg). Change any input and the result updates from the same shared formula.

## Substrate depth FAQ

**Q: How deep should aquarium substrate be?**

Bare-bottom tanks need no substrate. Sand-only beds typically sit at 1–2 in (≈ 2.5–5 cm); planted tanks usually run 2–3 in (≈ 5–7.5 cm) of aquasoil in the foreground with a thinner cap of sand or gravel on top.

**Q: What density should I use for sand?**

Wet sand is about 1.5 kg/L. Dry sand is closer to 1.4 kg/L, so pick 1.5 if you plan to rinse and soak the substrate before adding it. Gravel is a touch denser at roughly 1.6 kg/L.

**Q: Should I count dry or wet substrate weight?**

Count wet weight — the bag weight on the shelf is dry. Sand and gravel pick up a few percent water when rinsed, and aquasoil can roughly double its weight as it swells.

**Q: Do I need to subtract substrate from my water volume?**

Yes for planted tanks. Substrate occupies real volume below the water line, so subtract its volume from the tank capacity before computing water volume. The volume calculator has an optional substrate offset for exactly this case.

**Q: Does substrate volume change once it is underwater?**

Aquasoil swells noticeably when soaked, so the bed gets deeper after the first fill. Sand and gravel barely change. If you measure substrate dry, add roughly 10–20% to the depth for aquasoil so the bed ends up where you want it.

## References

Geometry is a rectangular box and density is a physical constant; the hobby references below cover how aquarists pick substrate depth and density in practice.

- [The Effect of Substrate on Water Quality in Ornamental Fish Tanks](https://doi.org/10.3390/ani12192679) — Vanderzwalmen M, Sánchez Lacalle D, Tamilselvan P, McNeill J, Delieuvin D, Behlouli K, et al., Animals (Basel), 2022.
- [Aquarium Co-Op — Substrate and aquasoil guide](https://www.aquariumcoop.com/) — Aquarium Co-Op, Aquarium Co-Op. Hobby reference for substrate depth conventions and the wet-vs-dry weight difference across sand, gravel, and aquasoil.
- [The Spruce Pets — choosing aquarium substrate](https://www.thesprucepets.com/aquarium-supplies-5082682) — The Spruce Pets, The Spruce Pets. Pet-care reference confirming the depth ranges for planted and fish-only tanks and the typical sand/gravel densities.
- [LiveAquaria — substrate and aquascaping](https://www.liveaquaria.com/) — LiveAquaria, LiveAquaria. Live-plant retailer whose substrate depth and density guides back the 5–7 cm planted-tank convention used on this page.
- [TFH Magazine — substrate volume references](https://www.tfhmagazine.com/) — TFH Magazine, TFH Magazine. Long-running aquarium hobby publication whose substrate tables back the typical depth and density values shown above.
- [Reef2Reef — substrate and sand-bed weight references](https://www.reef2reef.com/) — Reef2Reef, Reef2Reef. Marine aquarium community whose wet sand density tables back the ≈1.5 kg/L figure used in the worked example.
- [RSPCA — aquatic pet welfare (substrate and environment)](https://www.rspca.org.uk/adviceandwelfare/pets/aquatic) — RSPCA, RSPCA. Welfare charity guidance on substrate choice for aquatic pets, used to confirm the planted-tank depth range.
- [FishBase — species habitat substrate notes](https://www.fishbase.org/) — FishBase, FishBase. Species database with habitat substrate notes (sand, gravel, mud) for thousands of freshwater fish.

_Educational resource, not veterinary advice. PetGuideCalc — https://petguidecalc.com_