Concrete Thickness Calculator
Order 1.28-1.36 yd³
Plan volume 1.23 yd³ (33.33 ft³); range = NRMCA CIP-8 4-10% ordering allowance.
Buying bags instead: 62 × QUIKRETE 80 lb or 62 × SAKRETE 80 lb, at the yield each manufacturer publishes.
- Volume is plan geometry; NRMCA CIP 8 says order 4-10% over plan (subgrade, forms, spillage).
- A 1/8" thickness variation on a 4" slab is a ±3% volume swing; measure thickness honestly.
- Ready-mix increments and short-load fees are vendor practice; confirm with your plant.
- A 80 lb bag yields approximately 0.6 ft³, published identically by QUIKRETE and SAKRETE, so 62 bags including the ordering allowance. Whole-bag round-up.
Why This One Is Different
Pick the wrong thickness and you either pour a driveway that cracks under a delivery truck or a sidewalk with material you didn't need to buy. Thickness is the single input that swings a concrete order the most. A slab poured at 4-1/8 inches instead of a planned 4 inches isn't a rounding error; that eighth of an inch alone shifts total volume by roughly 3%, which is why a measured thickness, not a number pulled from memory, belongs in the field below. This calculator lets you compare thickness options side by side and see the yardage difference before concrete is on the truck.
Where the Numbers Come From
- A 1/8" thickness variation on a 4" slab is approximately a 3% swing in total volume, since thickness error compounds faster than length or width error on typical slabs. Source: NRMCA CIP 8 convention, applied via construction-estimating engine
- 4-inch slabs are a common trade default for walkways and patios, and 5-6 inches for driveways carrying vehicle loads. This is a trade convention, not a code minimum, and local code or soil conditions can require more. Source: trade convention, labeled as such (not codified in a standard)
- Order 4-10% more concrete than your plan-derived volume no matter which thickness you settle on, since form deflection and subgrade irregularity affect every pour the same way, per NRMCA guidance. Source: NRMCA, CIP 8, Discrepancies in Yield (2021 reprint)
More Questions
How much does adding an inch of thickness affect material cost?
More thickness means proportionally more concrete: going from 4 to 5 inches adds roughly 25% more for the same footprint. Run both thicknesses through this calculator to see the exact yardage and cost difference for your dimensions.
Related Calculators
Formulas, waste factors, and cost models on this page follow the sourced conventions on our methodology page. Estimates only; verify with your supplier and local code. Quantities are US customary units and materials are US nominal sizes, so a 2x4 measures 1.5 by 3.5 inches and a cubic yard is 27 cubic feet. Outside the US the arithmetic still holds but the stock sizes differ, and converting the result does not convert the assumption.