How much gravel for a 33 gallon long tank?
48 × 13 × 13 in · freshwater planning
33 gallon long · gravel & substrate
The working
48 × 13 × 2 = 1,248 in³. Divide by 1,728 and multiply by 100 lb/ft³ = 72.22 lb. Round up to 4 bags of 20 lb.
| Depth | Gravel lb / 20 lb bags | Sand lb / 20 lb bags | Aquasoil lb / L |
|---|---|---|---|
| 1 in | 36.11 / 2 | 36.11 / 2 | 21.67 / 10.23 |
| 2 in | 72.22 / 4 | 72.22 / 4 | 43.33 / 20.45 |
| 3 in | 108.33 / 6 | 108.33 / 6 | 65 / 30.68 |
First decisions for this medium setup
The 624 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.
33 gallon long equipment and layout plan
A low, extended rectangle puts more of the layout along a horizontal swimming lane. The 48 × 13-inch base has an aspect ratio of 3.69:1. A lid or light must span roughly 48 inches; measure rim openings and bracket adjustment before ordering.
| Level bed | Sand bags, rounded up | Aquasoil bags, rounded up |
|---|---|---|
| 1 in | 36.11 lb / 2 × 20 lb | 10.23 L / 2 × 9 L |
| 2 in | 72.22 lb / 4 × 20 lb | 20.45 L / 3 × 9 L |
| 3 in | 108.33 lb / 6 × 20 lb | 30.68 L / 4 × 9 L |
The rear bank can rise 2 inches across the 13-inch width: a 15.38% slope. Keeping the front at 1 inch and the back at 3 uses the same 20.45 L as a flat two-inch bed across the full 48-inch length. Aquasoil is sold here in hypothetical 9 L bags; check the actual package.
Moving up from the 30 gallon changes square inches of substrate coverage from 432 to 624: an increase of 44.44%. Budget for the larger requirement rather than reusing the smaller plan unchanged.
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 2.19 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 48 by 13 inches.
- Choose an average depth, allowing for slopes and hardscape.
- Calculate volume and mass as above; buy about 4 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 33 gallon long calculation use?
It uses a rounded 48 × 13 × 13 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the gravel & substrate estimate for a 33 gallon long tank?
72.22 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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