How to use this calculator
- Enter shed dimensions. Standard sizes: 8×8 (64 ft²), 8×10 (80 ft²), 10×10 (100 ft²), 10×12 (120 ft²), 12×16 (192 ft²).
- Set thickness. 4 in for storage and small workshop sheds; 6 in if storing heavy equipment or tractors.
- Pick units. Imperial (ft + in) is standard for U.S. sheds. Metric option available.
- Read the result. Cubic yards (for ready-mix delivery), 60lb and 80lb bag count (for bagged pours), and total project cost when price is entered.
Formula
Volume (yd³) = Length × Width × Thickness ÷ 27
Worked example
A 10 × 12 ft × 4 in slab for a shed pad: 1.48 cubic yards (40 ft³). For a bagged pour, that's about 90 bags of 60-lb pre-mix or 67 bags of 80-lb. Most shed pads are bagged because the volume is below the ready-mix short-load threshold.
Common project sizes
Quick reference for the most common shed foundation calculator use cases. Use these as a sanity check on your calculator inputs.
| Project | Dimensions | Result |
|---|---|---|
| 8 × 8 ft × 4 in slab | 64 ft² | 0.79 yd³ · 48 bags 60lb · 36 bags 80lb |
| 8 × 10 ft × 4 in slab | 80 ft² | 0.99 yd³ · 60 bags 60lb · 45 bags 80lb |
| 10 × 12 ft × 4 in slab | 120 ft² | 1.48 yd³ · 90 bags 60lb · 67 bags 80lb |
| 12 × 16 ft × 4 in slab | 192 ft² | 2.37 yd³ · 144 bags 60lb · 108 bags 80lb |
2026 cost reference
Typical retail price range in the United States for shed foundation. Local pricing varies by region, supplier, and grade — confirm with two or three quotes before ordering.
Per cubic yard (delivered)
$135 – $180
Standard 3,000 PSI ready-mix in 2026. For shed pads under 1.5 yd³, expect a $60–$150 short-load fee. Bagged pre-mix breakeven: about 1 yd³.
Tips for accurate results
- For sheds under 100 ft² in most U.S. jurisdictions, no permit is needed — but always check before pouring.
- A compacted gravel pad (4 in of crushed stone) is a faster, cheaper alternative to concrete for prefab sheds. Drains better, costs 60–70% less.
- For sheds on a slope, use pier blocks (concrete or precast) rather than a full slab — easier to level and skip frost-line digging.
- Always slope the pad 1/4" per ft away from the shed door to prevent water pooling.
- In freezing climates, a shed slab should sit on a 4-in compacted gravel base for drainage.
When to consult a pro
A small shed pad (under 100 ft²) is one of the more workable DIY concrete projects. The risks: getting the pad level (use a string line), preventing slab cracks (control joints every 8–10 ft, and proper curing for 7+ days), and drainage. For sheds over 12×16 or any heated/insulated structure, hire a pro — the extra precision pays back in flat surfaces and crack-free finishes.