MaterialScopeHow this calculation works
Enter measurements above to see the worked calculation.
Example: a 20 × 12-foot patio
At 4 inches thick, the geometric volume is 80 cubic feet, or 2.96296 cubic yards. A 10% allowance produces 3.25926 cubic yards, displayed as 3.26. If your supplier sells quarter-yard increments, that would round up to 3.50 cubic yards. Confirm the increment rather than assuming it.
Concrete for common slab sizes at 4 inches
Find your slab below, or enter its exact dimensions above. The same method applies to every size: length × width × thickness in feet, divided by 27.
| Slab size | Net concrete | With 10% extra | 80-lb bags* |
|---|---|---|---|
| 10 × 10 ft | 1.23 yd³ | 1.36 yd³ | 62 |
| 10 × 12 ft | 1.48 yd³ | 1.63 yd³ | 74 |
| 12 × 12 ft | 1.78 yd³ | 1.96 yd³ | 88 |
| 12 × 14 ft | 2.07 yd³ | 2.28 yd³ | 103 |
| 12 × 16 ft | 2.37 yd³ | 2.61 yd³ | 118 |
| 10 × 20 ft | 2.47 yd³ | 2.72 yd³ | 123 |
| 12 × 20 ft | 2.96 yd³ | 3.26 yd³ | 147 |
| 12 × 24 ft | 3.56 yd³ | 3.91 yd³ | 176 |
| 16 × 20 ft | 3.95 yd³ | 4.35 yd³ | 196 |
| 20 × 20 ft | 4.94 yd³ | 5.43 yd³ | 245 |
| 20 × 24 ft | 5.93 yd³ | 6.52 yd³ | 294 |
| 24 × 24 ft | 7.11 yd³ | 7.82 yd³ | 352 |
*Bag counts include the 10% allowance and assume 0.60 ft³ per bag. Ready-mix and bags are alternatives. For a 5- or 6-inch slab, multiply the cubic yards by 1.25 or 1.5, or enter the thickness above for exact bag counts. Worked guides: 10x10, 12x12 and 20x20 slabs.
Volume, allowance and an order are different
Net volume is the space to fill. The allowance adds extra material for variation in excavation, forms and handling. A supplier may then round the order to its available increments. Our decimal result does not apply that final supplier rounding. For multiple sections, calculate each section and add the unrounded volumes before ordering.
Bag equivalents are alternatives
The displayed 60-lb and 80-lb equivalents use illustrative yields of 0.45 and 0.60 cubic feet. They are alternatives to a ready-mix delivery, not additional materials. A bag’s weight alone does not determine its yield. Check the product you will actually buy.
Product reference: QUIKRETE concrete mix technical data. Confirm the current label for your chosen product.
Choose how to buy your concrete
Compare bagged concrete with a ready-mix delivery, including handling and fees. If buying bags, see our QUIKRETE vs. Sakrete product comparison for published yields and a project-cost example.
Make the estimate your own
Measure the actual area, choose your product and update the allowance. Costs use the price you enter. Delivery, tax, labor and preparation are excluded unless this tool has a separate field for them. The result rounds whole packages up; displayed decimal quantities are not supplier order increments.
Before you order
- Check dimensions and units, including depth and openings.
- Confirm the selected product’s coverage, yield or density.
- Ask your supplier about package sizes, minimum orders and delivery access.
- Keep a copy of your measurements with your material plan.
Method v1.0 · Updated October 23, 2026. Read our methodology.