Concrete Slab Calculator
Estimate how much concrete you need for a rectangular slab — in cubic yards and cubic meters — with an optional waste allowance for spillage and uneven subgrade.
Result
| Volume | |
| Volume (metric) | |
| Order quantity (with waste) |
Units & conversions used
Imperial inputs are feet and inches; results are shown in cubic feet, cubic yards (1 yd³ = 27 ft³) and cubic meters (1 ft³ = 0.02832 m³). Metric inputs are converted first: 1 m = 3.28084 ft, 1 cm = 0.3937 in.
Formula & source
V(yd³) = V(ft³) ÷ 27
Source: basic rectangular-prism geometry. The 5–10% waste allowance is standard ready-mix ordering practice (covers spillage, form deflection and subgrade unevenness); it is an industry rule of thumb, not a code requirement. Structural design (rebar, thickness for loads) is governed by ACI 318 and local codes — this calculator does not cover that.
Worked example (you can verify by hand)
Input: 10 ft × 12 ft slab, 4 in thick, 7% waste.
- Thickness in feet: 4 ÷ 12 = 0.3333 ft
- Volume: 10 × 12 × 0.3333 = 40.00 ft³
- Cubic yards: 40 ÷ 27 = 1.4815 yd³
- With 7% waste: 1.4815 × 1.07 = 1.5852 yd³
Expected output: 1.48 yd³ (1.59 yd³ with waste), 1.13 m³ (1.21 m³ with waste).
Limitations — what this cannot do
- This estimates volume only. It does not design slab thickness, reinforcement, joint spacing or subgrade preparation — those follow ACI 318 and local building codes; consult a structural engineer for load-bearing slabs.
- Assumes a perfectly rectangular slab of uniform thickness. Irregular shapes need to be broken into rectangles (or use our column/footing calculators for those parts).
- Ready-mix suppliers have minimum load charges; small orders may cost more per yard.
FAQ
How many cubic yards of concrete do I need for a 10×12 slab at 4 inches?
40 ft³ ÷ 27 = 1.48 yd³ before waste. Order about 1.6 yd³ with a 7% allowance. Most suppliers round up to the nearest quarter or half yard.
Should I add extra for waste?
Yes — 5–10% is standard practice. Forms flex, subgrade is never perfectly level, and some concrete sticks to the chute and wheelbarrow. It is cheaper than a short load and a cold joint.
How thick should my concrete slab be?
This calculator cannot answer that — thickness depends on loads and soil. As a rough reference, 4 in is common for patios and walkways, 5–6 in for residential driveways, but confirm with local code or an engineer.
How do I convert cubic feet to cubic yards?
Divide by 27. One cubic yard = 27 cubic feet (3 ft × 3 ft × 3 ft).
How much does it cost to pour a concrete slab?
In the US, a basic 4-inch concrete slab typically costs $4–$8 per square foot installed (materials plus labor), based on commonly published 2025–2026 contractor pricing guides. Decorative or stamped finishes usually run $8–$18+ per square foot. These are broad ranges — actual quotes vary widely by region and job conditions. The biggest cost drivers are:
- Slab thickness — a 6-inch driveway slab uses ~50% more concrete than a 4-inch patio slab.
- Site preparation — grading, excavation, and removing old concrete or sod add labor and disposal cost.
- Reinforcement — wire mesh or rebar adds material and labor versus plain concrete.
- Finish — a basic broom finish is cheapest; stamped, stained, or exposed-aggregate finishes cost more.
- Access and region — tight sites that need pumping, and high-cost labor markets, push prices up.
Get at least two or three local quotes before budgeting — use the calculator above to know your cubic yards first, so you can sanity-check any quote.
How long does concrete take to cure?
| Stage | Typical timing | What it means |
|---|---|---|
| Initial set | 24–48 hours | Surface hardens; keep all traffic off |
| Foot traffic | ~7 days | About 70% of design strength; light use OK |
| Drive / heavy loads | ~28 days | Reaches full design strength |
These are standard industry timelines for normal Portland-cement concrete cured at moderate temperatures. Keep the slab moist (or covered) during the first week — concrete that dries out too fast can lose significant strength. Cold weather slows curing; hot, windy weather speeds surface drying and raises cracking risk.