How much gravel for a 120 gallon tank?
48 × 24 × 24 in · freshwater planning
120 gallon · gravel & substrate
The working
48 × 24 × 2 = 2,304 in³. Divide by 1,728 and multiply by 100 lb/ft³ = 133.33 lb. Round up to 7 bags of 20 lb.
| Depth | Gravel lb / 20 lb bags | Sand lb / 20 lb bags | Aquasoil lb / L |
|---|---|---|---|
| 1 in | 66.67 / 4 | 66.67 / 4 | 40 / 18.88 |
| 2 in | 133.33 / 7 | 133.33 / 7 | 80 / 37.76 |
| 3 in | 200 / 10 | 200 / 10 | 120 / 56.63 |
120 gallon equipment and layout plan
A low, extended rectangle puts more of the layout along a horizontal swimming lane. The 48 × 24-inch base has an aspect ratio of 2:1. 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 | 66.67 lb / 4 × 20 lb | 18.88 L / 3 × 9 L |
| 2 in | 133.33 lb / 7 × 20 lb | 37.76 L / 5 × 9 L |
| 3 in | 200 lb / 10 × 20 lb | 56.63 L / 7 × 9 L |
For this large base, budget 37.76 L for a continuous 1-to-3-inch front-to-back slope. The shallow edge runs 48 inches, with the rise extending over 24 inches. Hardscape or terraces change the covered area. Buy soil by litres; estimated bulk density does not establish how much a particular package weighs.
Moving up from the 110 gallon changes square inches of substrate coverage from 864 to 1,152: an increase of 33.33%. 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 1.11 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
First decisions for this large setup
For this 48-inch run, distribute unopened bags along the work area before filling. Calculate planted zones separately if only part of the base needs deep soil. A shallow open sand lane and deeper rear planting area require an area-weighted average; the full-footprint table deliberately assumes uniform coverage.
How to use this plan
- Measure the inside footprint; this plan uses 48 by 24 inches.
- Choose an average depth, allowing for slopes and hardscape.
- Calculate volume and mass as above; buy about 7 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 120 gallon calculation use?
It uses a rounded 48 × 24 × 24 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.
What is the gravel & substrate estimate for a 120 gallon tank?
133.33 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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