How much gravel for a 20 gallon extra high tank?

20 × 10 × 24 in · freshwater planning

23.15 lb gravel for a 2-inch bed

20 gallon extra high · gravel & substrate

20 gallon extra high equipment and layout plan

Height is the defining feature; the short base limits horizontal layouts. The 20 × 10-inch base has an aspect ratio of 2:1. A lid or light must span roughly 20 inches; measure rim openings and bracket adjustment before ordering.

Level bed	Sand bags, rounded up	Aquasoil bags, rounded up
1 in	11.57 lb / 1 × 20 lb	3.28 L / 1 × 9 L
2 in	23.15 lb / 2 × 20 lb	6.55 L / 1 × 9 L
3 in	34.72 lb / 2 × 20 lb	9.83 L / 2 × 9 L

To build a slope along the 20-inch front, calculate a shallow 1-inch strip and a deep 3-inch rear bank. Their average depth is 2 inches if the slope is linear across 10 inches. Buy 6.55 L before accounting for rocks. Soil counts assume 9 L packages, not a guaranteed bag weight.

The 20 gallon high uses 288 square inches of substrate coverage; this tank uses 200, a reduction of 30.56%. Scale the plan down to the actual dimensions and capacity.

First decisions for this small setup

Lay out the 20-inch front edge before pouring substrate. Keep a clear strip where the siphon will reach, and place heavy hardscape securely rather than relying on loose gravel to hold it upright. Rounded-up bag totals leave surplus: do not pour every bag in just because it was purchased.

The working

20 × 10 × 2 = 400 in³. Divide by 1,728 and multiply by 100 lb/ft³ = 23.15 lb. Round up to 2 bags of 20 lb.

Depth	Gravel lb / 20 lb bags	Sand lb / 20 lb bags	Aquasoil lb / L
1 in	11.57 / 1	11.57 / 1	6.94 / 3.28
2 in	23.15 / 2	23.15 / 2	13.89 / 6.55
3 in	34.72 / 2	34.72 / 2	20.83 / 9.83

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 1.16 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 20 by 10 inches.
Choose an average depth, allowing for slopes and hardscape.
Calculate volume and mass as above; buy about 2 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 20 gallon extra high calculation use?

It uses a rounded 20 × 10 × 24 inch rectangle. Actual dimensions vary by brand and frame; measure your own tank.

What is the gravel & substrate estimate for a 20 gallon extra high tank?

23.15 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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