Concrete Slab Calculator
Estimate concrete volume, bags, and cost for garage floors, patios, driveways, and foundation slabs. Enter slab dimensions and thickness for accurate yardage.
Last updated 2026-08-21
What Is a Concrete Slab Calculator?
A concrete slab calculator estimates the volume, bags, and cost for flat concrete surfaces like garage floors, patios, driveways, and foundation slabs. You enter the slab length, width, and thickness, and it returns the cubic yards of ready-mix you need. It is the quickest way to size a pour before you order concrete or rent a mixer.
How It Works
Volume (ft³) = Length × Width × (Thickness ÷ 12). Cubic yards = Volume ÷ 27.
Example
A 12 ft × 12 ft garage slab at 4 in thick: 12 × 12 × (4 ÷ 12) = 48 ft³ ≈ 1.78 cubic yards before waste.
How to Calculate
- Measure the slab length and width in feet. For a 12 ft by 12 ft garage slab, enter 12 and 12.
- Choose the slab thickness in inches. A 4 in slab is common for garages, so enter 4.
- Enter a waste factor of 5 to 10% to account for spillage and form joints.
- The calculator finds the volume: 12 × 12 × (4 ÷ 12) = 48 cubic feet, or about 1.78 cubic yards before waste.
- Add 10% waste to order roughly 1.96 cubic yards, then check whether that is under the typical 9 to 10 yard truck minimum.
Concrete Slab Thickness Guidance
| Slab Type | Thickness | Notes |
|---|---|---|
| Walkway | 4 in | Standard for foot traffic |
| Patio | 4 in | Fine for most outdoor seating |
| Driveway | 4 to 6 in | Use 6 in for heavy vehicles |
| Garage floor | 4 in | 4 in suits most cars |
| Heavy load slab | 6 in or more | For large equipment or trucks |
Sources
Frequently Asked Questions
What thickness do I need?
4 in for most patios and walkways, 4–6 in for driveways, and 6 in or more for vehicle-heavy or load-bearing slabs.
Should I add rebar or mesh?
Most residential slabs use welded wire mesh or rebar on edges. Check local codes — it does not change the concrete volume.
How much does a concrete truck hold?
Typical trucks carry 9–10 cubic yards. If your slab is under that, you may pay a short-load fee.
Estimate the cost with the Concrete Cost Calculator or browse Concrete Calculators