How much gravel for a 37 gallon tank?
30 × 12 × 22 in · freshwater planning
37 gallon · gravel & substrate
The working
30 × 12 × 2 = 720 in³. Divide by 1,728 and multiply by 100 lb/ft³ = 41.67 lb. Round up to 3 bags of 20 lb.
| Depth | Gravel lb / 20 lb bags | Sand lb / 20 lb bags | Aquasoil lb / L |
|---|---|---|---|
| 1 in | 20.83 / 2 | 20.83 / 2 | 12.5 / 5.9 |
| 2 in | 41.67 / 3 | 41.67 / 3 | 25 / 11.8 |
| 3 in | 62.5 / 4 | 62.5 / 4 | 37.5 / 17.7 |
First decisions for this medium setup
The 360 square inches of floor make substrate depth a meaningful purchase decision. Compare the one-inch and three-inch rows before committing to a deep planted layout. Terraces and retaining rocks can keep a rear bank from spreading, but their occupied footprint reduces the amount of loose substrate needed.
37 gallon equipment and layout plan
This upright rectangle adds vertical room without a wider bottom. The 30 × 12-inch base has an aspect ratio of 2.5:1. A lid or light must span roughly 30 inches; measure rim openings and bracket adjustment before ordering.
| Level bed | Sand bags, rounded up | Aquasoil bags, rounded up |
|---|---|---|
| 1 in | 20.83 lb / 2 × 20 lb | 5.9 L / 1 × 9 L |
| 2 in | 41.67 lb / 3 × 20 lb | 11.8 L / 2 × 9 L |
| 3 in | 62.5 lb / 4 × 20 lb | 17.7 L / 2 × 9 L |
The rear bank can rise 2 inches across the 12-inch width: a 16.67% slope. Keeping the front at 1 inch and the back at 3 uses the same 11.8 L as a flat two-inch bed across the full 30-inch length. Aquasoil is sold here in hypothetical 9 L bags; check the actual package.
The 33 gallon long uses 624 square inches of substrate coverage; this tank uses 360, a reduction of 42.31%. Scale the plan down to the actual dimensions and capacity.
Assumptions and limits
The old 1 lb/gal for roughly 1 inch and 1.5–2 lb/gal for 2 inches rules are loose shopping shortcuts. Here a 2-inch bed is 1.13 lb per nominal gallon. Footprint and bulk density explain the difference. Gravel and sand use 100 lb/ft³; aquasoil uses 60. Check bag coverage; grain size and moisture change density.
Bulk densities are stated planning assumptions; litre conversion: NIST conversion tables
How to use this plan
- Measure the inside footprint; this plan uses 30 by 12 inches.
- Choose an average depth, allowing for slopes and hardscape.
- Calculate volume and mass as above; buy about 3 20 lb bags for a level 2-inch gravel bed.
Adjust measurements with the gravel & substrate calculator
Questions before you buy
What dimensions does this 37 gallon calculation use?
It uses a rounded 30 × 12 × 22 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the gravel & substrate estimate for a 37 gallon tank?
41.67 lb gravel for a 2-inch bed
Equipment to check
Compare aquarium substrate. Check dimensions, capacity and product instructions before buying.
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