Free tool
Concrete calculator
Add slabs and footings, round columns or post holes, and a waste allowance. You get cubic yards for a ready-mix order and the number of 40, 60 or 80 lb bags, using QUIKRETE's published yields.
Concrete needed
1.9 cu yd51.2 cu ft including 10% waste
- Slabs and footings
- 40 cu ft
- Columns and holes
- 6.5 cu ft
- Ready-mix order
- 2 cu yd
- 80 lb bags
- 86
- 60 lb bags
- 114
- 40 lb bags
- 171
Bag yields from QUIKRETE Concrete Mix: 0.60, 0.45 and 0.30 cu ft. Ready-mix rounded up to the next quarter yard.
1.9 cubic yards (51.2 cubic feet) including 10% waste: 86 eighty-pound, 114 sixty-pound or 171 forty-pound bags.
How it's calculated
- Slab or footing (cu ft) = length × width × thickness (in) ÷ 12
- Round column or hole (cu ft) = π × (diameter ÷ 2)² × depth, in feet, × count
- With waste = total × (1 + waste %)
- Cubic yards = cubic feet ÷ 27
- Bags = cubic feet ÷ bag yield (0.30, 0.45 or 0.60 cu ft), rounded up
How to use it
- 1Add slabs and footings. Enter each slab, pad or footing as length × width in feet and thickness in inches.
- 2Add round pours. Enter round columns or post holes as diameter and depth in inches, and how many.
- 3Set waste. Add an allowance for uneven subgrade, spillage and form bulges.
- 4Order. Use cubic yards for ready-mix, rounded up to the next quarter yard, or the bag count for small pours.
Worked example
A 10 × 12 ft slab 4 inches thick, plus four post holes 10 inches across and 36 inches deep, with 10% waste.
- Slab = 10 × 12 × 4 ÷ 12 = 40 cu ft
- Holes = π × (5 ÷ 12)² × 3 × 4 = 6.54 cu ft
- With waste = 46.54 × 1.10 = 51.2 cu ft
- Cubic yards = 51.2 ÷ 27 = 1.9 cu yd
- Bags = 51.2 ÷ 0.60 = 86 eighty-pound bags (or 114 sixty-pound, 171 forty-pound)
Order 2 cubic yards of ready-mix, or 86 eighty-pound bags.
Sources
- QUIKRETE, Concrete Mix No. 1101 data sheet. Accessed 2026-11-03.
Yield: a 40 lb bag makes about 0.30 cu ft, a 60 lb bag about 0.45 cu ft and an 80 lb bag about 0.60 cu ft (50 lb: 0.375; 90 lb: 0.675).
- Vertigraph (takeoff and estimating software), How to calculate concrete yardage. Accessed 2026-11-03.
Volume = length × width × thickness in feet, divided by 27 for cubic yards. Waste allowance: 5–8% for large simple slabs, 10% as a general default, 12–15% for complex pours; round up to the next quarter yard. The calculator defaults to 10%.
FAQ
Concrete calculator questions
Have a question we didn't cover? Book a demo and ask a product specialist.
How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet. With QUIKRETE's yields that's 45 eighty-pound bags (0.60 cu ft each), 60 sixty-pound bags or 90 forty-pound bags, before waste.
How much extra concrete should I order?
Estimating guides commonly use 5–10%: the low end for flat, well-formed slabs and 10% or more for uneven subgrade, footings and small awkward pours. Running short mid-pour costs far more than a little extra.
When should I use ready-mix instead of bags?
Past a yard or so, mixing 45 or more bags by hand is slow and hard to finish before the concrete sets. Ready-mix suppliers often have minimum loads or short-load fees, so check before ordering a small amount.
Does the post hole volume subtract the post?
No. Round pours are figured as solid cylinders, which suits columns and footings. For fence posts set in concrete, the fence calculator subtracts the post.
Is a 4-inch slab thick enough?
Four inches is common for walks and patios; driveways and slabs that carry vehicles are often thicker. Follow your local code and the job's spec.
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