Concrete calculator: cubic yards and bags
Pick the shape, enter the size and how many. You get cubic feet, cubic yards, bag counts and a rough job price. Everything stays in your browser.
Your estimate
- Volume (before waste)
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- Cubic yards (with your waste setting)
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- Ready-mix order, rounded up to ¼ yard
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- Or 80 lb bags (≈ 0.60 cu ft each)
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- Or 60 lb bags (≈ 0.45 cu ft each)
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- Concrete cost
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- Labor (rough)
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- Rough job total
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Estimates only. Bag yields are typical label figures; check your bag. Uneven grade, forms and over-excavation change the real amount. Rebar, mesh, gravel base and forms are not included.
How to measure for concrete
- Slab: measure length and width in feet and the thickness in inches. Check thickness in a few spots; low spots in the base add up fast.
- Footing: add up the total run of the footing in feet, then the width and depth in inches.
- Round column or post hole: measure the diameter and depth in inches, and count the holes.
- Leave the 10% waste box on unless your grade and forms are very accurate.
Concrete for common slab sizes
Cubic yards without and with 10% waste, and 80 lb bags (with waste). Computed with the same formula as the calculator above.
| Slab | Thickness | Cubic yards | With 10% | 80 lb bags |
|---|---|---|---|---|
| 10 × 10 ft | 4 in | 1.23 yd³ | 1.36 yd³ | 62 |
| 12 × 12 ft | 4 in | 1.78 yd³ | 1.96 yd³ | 88 |
| 10 × 20 ft | 4 in | 2.47 yd³ | 2.72 yd³ | 123 |
| 20 × 20 ft | 4 in | 4.94 yd³ | 5.43 yd³ | 245 |
| 24 × 24 ft | 4 in | 7.11 yd³ | 7.82 yd³ | 352 |
| 10 × 10 ft | 6 in | 1.85 yd³ | 2.04 yd³ | 92 |
| 12 × 12 ft | 6 in | 2.67 yd³ | 2.93 yd³ | 132 |
| 10 × 20 ft | 6 in | 3.70 yd³ | 4.07 yd³ | 184 |
| 20 × 20 ft | 6 in | 7.41 yd³ | 8.15 yd³ | 367 |
| 24 × 24 ft | 6 in | 10.67 yd³ | 11.73 yd³ | 528 |
Bags per post hole (36 inches deep)
Volume of the full hole, without subtracting the post or adding waste. The post takes up some of the hole, so this leaves a little extra.
| Hole diameter | Volume | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 6 in | 0.59 cu ft | 1 | 2 |
| 8 in | 1.05 cu ft | 2 | 3 |
| 10 in | 1.64 cu ft | 3 | 4 |
| 12 in | 2.36 cu ft | 4 | 6 |
Ready-mix or bags?
Bags are handy for post holes and small pads. For bigger pours, ready-mix by the yard is usually less work and gives a more consistent pour. Many suppliers have a minimum order or a short-load fee, so ask before you order a small amount.
One cubic yard is 27 cubic feet. Ready-mix is usually ordered in quarter- or half-yard steps; the calculator rounds up to the next quarter yard.
What this calculator leaves out
Gravel base, forms, rebar or wire mesh, vapor barrier, finishing, sealing and permits are not included. Slab thickness, footing size and reinforcement should follow your local code and any plans or engineer’s specs.
Questions
How many cubic yards for a 10 × 10 slab, 4 inches thick?
That slab is about 33.3 cubic feet, or about 1.23 cubic yards. With 10% added for waste it is about 1.36 cubic yards, so many contractors would order 1.5 yards.
How many 80 lb bags make a yard of concrete?
A typical 80 lb bag makes about 0.60 cubic feet, so one cubic yard (27 cubic feet) takes about 45 bags. A 60 lb bag makes about 0.45 cubic feet, so about 60 bags per yard. Check the yield printed on your bag.
How thick should a concrete slab be?
Four inches is common for patios and sidewalks. Driveways and slabs that carry heavier loads are often thicker. Follow your local code and any plans for the job.
Should I add extra for waste?
Yes. Adding about 10% covers spillage, uneven grade and form movement. It is much easier to have a little left over than to run short in the middle of a pour.
Is this calculator free? Does it save my numbers?
Yes, it is free and needs no sign-up. Nothing is saved or sent anywhere; the math runs in your browser and is gone when you close the page.
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