How Many Bags of Concrete for a 10x12 Slab?
A 10×12 foot slab covers 120 square feet — a common shed pad or small patio size. Bag count depends on thickness: a 4-inch pour needs about 74 eighty-pound bags; a 6-inch pour needs about 110. Full math for both depths below using the same 10% waste factor as our 10×10 slab guide.
Last updated: June 30, 2026
Use the Slab Calculator →Steps
- Calculate base volume — Multiply 10 ft × 12 ft × (thickness in ÷ 12). A 4-inch slab = 40 ft³; a 6-inch slab = 60 ft³.
- Add 10% waste — Multiply base volume by 1.10. A 4-inch slab becomes 44 ft³; a 6-inch slab becomes 66 ft³.
- Convert to 80 lb bags — Divide adjusted volume by 0.60 ft³ per 80 lb bag and round up. Result: 74 bags (4 in) or 110 bags (6 in).
4-inch slab — 120 sq ft patio
Area: 10 ft × 12 ft = 120 ft². Thickness 4 ÷ 12 = 0.333 ft.
Base volume = 120 × 0.333 = 40 ft³. With 10% waste: 40 × 1.10 = 44 ft³.
Bags = 44 ÷ 0.60 = 73.3 → round up to 74 bags of 80 lb mix (~1.63 yd³ with waste).
6-inch slab — heavy-duty pad
Same 120 ft² area; thickness 6 ÷ 12 = 0.5 ft. Base volume = 120 × 0.5 = 60 ft³.
With 10% waste: 60 × 1.10 = 66 ft³. Bags = 66 ÷ 0.60 = 110 eighty-pound bags.
At about 2.44 yd³ with waste, ready-mix delivery is often worth comparing to bag labor.
Verify with the calculator
Enter 10 ft length, 12 ft width, and your thickness in our free slab calculator for an instant bag count and cubic yard total.
Frequently asked questions
- How many 80 lb bags for a 10x12 patio at 4 inches?
- About 74 bags. Volume is 10 × 12 × (4 ÷ 12) = 40 ft³. With 10% waste that is 44 ft³. At 0.60 ft³ per 80 lb bag, divide and round up to 74 bags.
- How many bags for a 10x12 slab at 6 inches?
- About 110 bags. Base volume is 60 ft³; with 10% waste that is 66 ft³. At 0.60 ft³ per bag: 66 ÷ 0.60 = 110 bags.
- 10x12 vs 10x10 — how many extra bags?
- At 4 inches with waste, a 10×12 slab needs about 12 more bags than a 10×10 (74 vs 62). The extra 20 sq ft of area drives the difference.