Concrete Slab Calculator
Calculate the cubic yards of concrete and total material cost for patios, driveways, and walkways. Enter slab dimensions, thickness, a waste factor, and your supplier's price per yard to get an instant estimate.
About this calculator
Concrete volume is measured in cubic yards. The base volume formula is: volume (yd³) = (length × width × (thickness / 12)) / 27, where thickness is entered in inches and dividing by 12 converts it to feet before dividing by 27 (the number of cubic feet per cubic yard). A waste factor (typically 1.05–1.10 for a 5–10% overage) is multiplied in to cover form spillage and uneven subgrades. The result is rounded up to the nearest hundredth of a cubic yard, then multiplied by price per cubic yard to give total material cost: cost = ⌈volume × wasteFactor × 100⌉ / 100 × pricePerYard. Ordering at least 5% extra is standard practice in the industry.
How to use
Pour a 12 ft × 20 ft patio, 4 inches thick, with a 1.05 waste factor and a concrete price of $150 per cubic yard. Base volume = (12 × 20 × (4 / 12)) / 27 = (12 × 20 × 0.333) / 27 = 80 / 27 ≈ 2.963 yd³. Apply waste: 2.963 × 1.05 = 3.111 yd³. Round up to nearest hundredth: 3.12 yd³. Total cost = 3.12 × $150 = $468.00. You would order 3.5 yd³ (minimum truck load increments) and budget approximately $468 for material alone, excluding labor.
Frequently asked questions
How many cubic yards of concrete do I need for a 10x10 slab at 4 inches thick?
A 10 ft × 10 ft slab at 4 inches thick requires (10 × 10 × (4/12)) / 27 = (100 × 0.333) / 27 ≈ 1.23 cubic yards. With a standard 5% waste factor, you should order about 1.30 cubic yards. Most ready-mix suppliers have a minimum load of 1 cubic yard, and short-load fees apply for orders under about 5 yards, so factor that surcharge into your budget. For very small slabs, buying premix bags may be more economical.
What waste factor should I use when calculating concrete for a slab?
A 5% waste factor (1.05) is adequate for simple rectangular slabs with good form work and a level subgrade. Use 8–10% (1.08–1.10) for irregular shapes, slabs with cutouts, or sites with an uneven compacted base. Running out of concrete mid-pour is a serious problem — you cannot stop and restart without creating a cold joint — so erring on the side of slightly more material is always the safer choice. Leftover concrete can be used for small footings, stepping stones, or fence posts.
How much does a cubic yard of concrete cost in 2024?
Ready-mix concrete in the United States typically costs $125–$200 per cubic yard for standard 3,000–4,000 PSI mixes, with prices varying by region, fuel surcharges, and additives. High-strength or fiber-reinforced mixes run $160–$250 per yard. Short-load fees ($75–$150) are added when your order is below the minimum load, usually 5–7 yards. Delivery, pump truck rental ($400–$800), and finishing labor are separate costs not included in the per-yard price, so request an all-in quote from your supplier.