Concrete Volume Calculator
Work out how much concrete a slab, patio, footing or driveway needs. Enter length and width in feet and thickness in inches; get cubic yards, cubic feet, cubic meters or the number of 40, 60 or 80 lb bags, with a waste allowance.
Last updated: October 2026
Concrete Needed
1.3 cu yd
Formula below · 2 sources (nrmca.org, quikrete.com) · Updated Oct 2026
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About this calculator
Concrete volume is length × width × thickness. With length and width in feet and thickness in inches, the volume in cubic feet is L × W × (T ÷ 12). Ready-mix concrete is sold by the cubic yard, and one cubic yard is 27 cubic feet, so cubic yards = cubic feet ÷ 27. A 10 ft × 10 ft patio 4 inches thick is 100 × 4 ÷ 12 = 33.3 cu ft, or 1.23 cu yd before any waste allowance.
How much extra to order
The volume you pour is almost always more than the plan dimensions suggest: forms bow, the subgrade is uneven, some concrete is spilled and some stays in the truck or wheelbarrow. The National Ready Mixed Concrete Association recommends ordering 4% to 10% more than the volume calculated from the plans. Use the low end for a well-formed slab on a level, compacted base and the high end for footings dug into soil or a first DIY pour.
Bags or ready-mix
Bagged concrete yields a fixed volume per bag. QUIKRETE's data sheet lists 0.30 cu ft for a 40 lb bag, 0.45 cu ft for 60 lb and 0.60 cu ft for 80 lb, so one cubic yard takes 45 bags of 80 lb mix. That is practical for post holes, small pads and repairs; for a cubic yard or more, mixing by hand is slow and a ready-mix delivery or a rented mixer is usually easier. The bag count is rounded up to whole bags.
Other shapes
For a round footing or column, use π × radius² × depth with all measurements in feet. Split an L-shaped slab into two rectangles and add the results. Steps, walls and thickened slab edges can be added the same way, one rectangle at a time.
| Thickness | Cubic yards | Cubic feet | 80 lb bags |
|---|---|---|---|
| 3.5 in | 1.08 | 29.2 | 49 |
| 4 in | 1.23 | 33.3 | 56 |
| 5 in | 1.54 | 41.7 | 70 |
| 6 in | 1.85 | 50 | 84 |
| 8 in | 2.47 | 66.7 | 112 |
How to use
Enter the length and width of the pour in feet and the thickness in inches, pick a waste allowance and choose how you want the answer. The default 10 ft × 10 ft slab, 4 in thick with 5% extra, needs 35 cu ft: 1.3 cubic yards, or 59 bags of 80 lb mix. A 24 ft × 24 ft garage floor 4 in thick with 10% extra needs 24 × 24 × 4 ÷ 12 × 1.10 ÷ 27 ≈ 7.8 cubic yards.
Frequently asked questions
How many cubic yards of concrete do I need for a 10x10 slab?
A 10 ft × 10 ft slab 4 inches thick is 33.3 cubic feet, or 1.23 cubic yards. With 5% extra that is about 1.3 cubic yards; at 6 inches thick it is 1.85 cubic yards before waste.
How many 80 lb bags of concrete make a cubic yard?
45. An 80 lb bag of QUIKRETE Concrete Mix yields about 0.60 cubic feet and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45 bags. With 60 lb bags (0.45 cu ft) you need 60, and with 40 lb bags (0.30 cu ft) 90.
How thick should a concrete slab be?
Four inches is the usual thickness for patios, walkways and residential garage floors. Driveways that carry heavier vehicles and slabs under equipment are often 5 to 6 inches. Footings and structural slabs follow the plans or local building code, so check those before ordering.
How much extra concrete should I order?
NRMCA recommends ordering 4% to 10% more than the volume calculated from the plan dimensions. Running short means waiting for a second truck while the first pour starts to set, which is far more costly than a small leftover.
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Sources & references
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