Shed manufacturers universally recommend a compacted gravel pad over resting skids on bare ground or concrete blocks. A gravel foundation supports the entire length of pressure-treated 4×4 floor runners evenly while draining rainwater away from the wood subfloor so it never rots.
Rule #1: Add a 12-Inch Perimeter Overhang on All Sides
Your gravel pad must extend at least 1 foot (12 inches) beyond the shed walls on all four sides—meaning you add 2 feet to both the length and width of your shed size:
| Shed Building Size | Required Gravel Pad Size | 4" Depth (#57 Stone) | 6" Depth (#57 Stone) |
|---|---|---|---|
| 8' × 10' Shed | 10' × 12' Pad (120 sq ft) | 2.20 tons (1.63 yd³) | 3.30 tons (2.44 yd³) |
| 10' × 12' Shed | 12' × 14' Pad (168 sq ft) | 3.08 tons (2.28 yd³) | 4.62 tons (3.42 yd³) |
| 10' × 16' Shed | 12' × 18' Pad (216 sq ft) | 3.96 tons (2.93 yd³) | 5.94 tons (4.40 yd³) |
| 12' × 16' Shed | 14' × 18' Pad (252 sq ft) | 4.62 tons (3.42 yd³) | 6.93 tons (5.13 yd³) |
| 12' × 20' Garage Shed | 14' × 22' Pad (308 sq ft) | 5.65 tons (4.18 yd³) | 8.47 tons (6.27 yd³) |
Run custom shed dimensions and timber border heights in our Shed Foundation Gravel Pad Calculator.