How Do I Calculate Yards of Concrete?

"Yards of concrete" almost always means cubic yards — the volume unit American ready-mix suppliers price by. To calculate it from raw dimensions, work in cubic feet first and divide by 27. The math is short; the unit conversion is what trips most people up.

The conversion you actually need

One cubic yard equals 27 cubic feet. So once you have a volume in cubic feet, divide by 27 to get yards. Alternatively, multiply by 0.037 — same answer, and easier on a phone calculator. In metric, one cubic yard equals 0.7646 cubic meters, and one cubic meter equals 1.308 cubic yards.

Example 1: A small driveway slab

Say you're pouring a 20 ft × 10 ft × 4 in driveway slab. The thickness is in inches, so first convert it to feet: 4 ÷ 12 = 0.333 ft. Then multiply: 20 × 10 × 0.333 = 66.7 ft³. Divide by 27: 66.7 ÷ 27 = 2.47 yd³.

Add 10% waste: 2.47 × 1.10 = 2.72 yd³. Round up to the supplier's nearest delivery increment (usually a quarter yard) and you'd order 2.75 yd³. A standard 9-yard ready-mix truck handles this with plenty of room to spare, but you'll pay a short-load fee since the load is under 5 yd³ — typically $50 to $150 in 2026 prices.

Example 2: A round footing

For a single deck pier — say 12 inches diameter and 48 inches deep — convert both to feet (1 ft and 4 ft). Apply the cylinder formula: π × (1/2)² × 4 = π × 0.25 × 4 = 3.14 ft³. Divide by 27 to get cubic yards: 3.14 ÷ 27 = 0.116 yd³. For a deck with twelve such piers, you'd need 12 × 0.116 = 1.40 yd³ — call it 1.50 with waste.

The fast slab shortcut

For slabs specifically, this one-line formula collapses every conversion: length-feet × width-feet × thickness-inches ÷ 324 = cubic yards. Why 324? Because 12 (inches per foot) × 27 (cubic feet per yard) = 324. So a 20 × 10 ft × 4 in slab is 20 × 10 × 4 ÷ 324 = 800 ÷ 324 = 2.47 yd³ — exactly what we got the long way.

Common dimensions, pre-calculated

• 10 × 10 × 4 in patio: 1.23 yd³ (1.36 with 10% waste)
• 12 × 12 × 4 in patio: 1.78 yd³ (1.96 with waste)
• 20 × 20 × 4 in two-car driveway: 4.94 yd³
• 24 × 24 × 4 in garage floor: 7.11 yd³ (round up to 8)
• 4 × 50 × 4 in sidewalk: 2.47 yd³

These assume a flat, prepared sub-grade and standard residential 4-in thickness. For driveways that will see RVs or heavy trucks, increase to 5–6 in and recalculate.

Watch for these mistakes

1. Mixing units. A "10 × 10 × 4" with thickness in inches is not 400 ft³. It's 33.3 ft³. Always convert first.
2. Forgetting waste. The supplier delivers exactly what's on the ticket. If you don't add 10% before ordering, you order short.
3. Rounding down. If the math says 2.47 yards, you order 2.50 minimum. Never round down on a concrete order.
4. Forgetting depth on footings. A 12-in deck pier hole is a 12-in diameter, not a 12-in width. A round footing is calculated as a cylinder, not a square prism.

Skip the math entirely with the concrete yard calculator. It handles every conversion automatically and gives the cubic-yard total plus weight, bag count, and an estimated truck-load.