Concrete slab calculator
You need
– cubic yards
– cu ft · – m³ · sq ft
- Ready-mix concrete ($160–$195/yd)
- –
- Installed by a contractor
- –
Short answer
For a slab, multiply length × width × thickness (in feet) and divide by 27. A 10 × 10 ft slab at 4 inches is 1.23 cubic yards, or 1.36 with 10% extra. Every extra inch of thickness adds 25% more concrete to a 4-inch slab.
| 10 × 10 ft × 4 in | 1.23 cu yd (33.3 cu ft) |
|---|---|
| 10 ft round × 4 in | 0.97 cu yd |
| Per 100 sq ft at 4 in | 1.23 cu yd |
| Installed basic slab (Sept 2026) | $10.63–$13.00 per sq ft[3] |
| Ready-mix | $160–$195+ per cu yd[2] |
| Thickness | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 4 in | 1.23 | 56 | 75 |
| 5 in | 1.54 | 70 | 93 |
| 6 in | 1.85 | 84 | 112 |
Slab examples
- 10 × 10 ft patio pad, 4 in: 1.23 cu yd (56 bags of 80 lb).
- 12 × 16 ft patio, 4 in: 2.37 cu yd.
- 24 × 24 ft garage slab, 4 in: 7.11 cu yd. At 6 in: 10.67 cu yd.
- 10 ft round slab, 4 in: 0.97 cu yd.
Prices for an installed slab are in the concrete slab cost guide.
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Frequently asked questions
How do I calculate how much concrete I need?
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Multiply length × width × thickness, all in feet, to get cubic feet, and divide by 27 to get cubic yards. Add 5–10% for waste and uneven ground.
How thick should a concrete slab be?
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4 inches is standard for patios, walkways and slabs for passenger cars. Driveways for heavier trucks or RVs, and slabs carrying heavy loads, are usually 5–6 inches. Structural slabs follow engineered or code requirements.
How much concrete for a 20×20 slab?
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A 20 × 20 ft slab at 4 inches needs 4.94 cubic yards, or 5.43 with 10% extra.
Sources
- [1]QUIKRETE, Concrete Mix No. 1101 data sheet (bag yields) (current data sheet)
- [2]ConcreteNetwork.com, Concrete Prices (updated July 14, 2026)
- [3]Homewyse, Cost to Install Cement Slab (September 2026 figures)
Prices are national ranges published by the sources above, not quotes. Your price depends on size, access, site preparation and local labor rates. The only way to know is to compare written quotes.