Concrete Slab Calculator
Last updated: February 2026
This concrete slab calculator outputs concrete volume in cubic yards, cubic feet, and cubic meters, plus an 80-lb bag estimate for smaller pours. Enter slab dimensions, thickness, and waste percentage to get an order-ready quantity. If you enter pricing in the results panel, it also estimates material cost for ready-mix and bagged concrete.
Pouring a slab? Use our Concrete Slab Reinforcement Guide to choose rebar vs wire mesh and common spacing rules.
To reduce random cracking, follow our Concrete Control Joints guide for spacing, depth, and saw-cut timing.
What is a Concrete Slab?
A concrete slab is a flat, horizontal surface made of poured concrete, commonly used for patios, driveways, garage floors, and foundations.
The results include cubic yards, cubic feet, cubic meters, and an 80-lb bag estimate for small pours. Adjust thickness to match use (patio vs garage), and plan extra waste for forms, spillage, or thickened edges. Reinforcement, subbase quality, and finishing time also affect performance and cost. If you are deciding on depth, a slab thickness guide can help set a baseline. Use this concrete slab calculator to sanity check orders and avoid coming up short on pour day.
Want the full estimate? Use the Concrete Project Estimator.
Typical Concrete Slab Costs (2026)
Installed slab pricing varies by project type, slab thickness, and site conditions. Use these ranges as planning benchmarks.
| Project Type | Installed Cost Range |
|---|---|
| Patio (4") | $10-$20 per sq ft |
| Driveway (5-6") | $12-$25 per sq ft |
| Garage Floor (6") | $15-$30 per sq ft |
Final price usually shifts with labor rates, site access, and finish complexity.
If you're deciding between a poured slab and a paver patio or driveway, see our Concrete vs Pavers guide to compare cost, drainage, and repairs.
Concrete Slab Thickness Rules (Snippet Nest)
- 4 inches - light foot traffic, patio
- 5 inches - standard driveways
- 6 inches - heavy loads (RV, trucks)
- More than 6 inches - engineered or structural design
Quick Rule of Thumb:Choose 4" for walkways/patios.
Choose 5-6" for driveways/garage floors.
Add reinforcement with rebar or wire mesh for slabs >100 sq ft or vehicle loads.
Before choosing your slab thickness, compare concrete and pavers in the Concrete vs Pavers guide.
Concrete Slab Thickness by Project Type
| Project Type | Recommended Thickness | PSI Strength |
|---|---|---|
| Patio / Walkway | 4 inches | 3,000 PSI |
| Driveway | 5-6 inches | 3,500-4,000 PSI |
| Garage Floor | 6 inches | 3,500-4,000 PSI |
| Shed Slab | 4-5 inches | 3,000 PSI |
| RV Pad | 6-8 inches | 4,000+ PSI |
Thickness increases with load weight, soil conditions, and freeze-thaw exposure.
Inputs
Tip: For small pours, waste of 5–10% is common. For complex forms, consider 10–15%.
Pro Tip: Round thickness up to the nearest 0.5 inch when planning forms and ordering to avoid coming up short.
Quick Reference: Bags per Cubic Yard
| Bag Size | Approx Bags per 1 yd^3 | Typical Yield per Bag |
|---|---|---|
| 60 lb | ~60 bags | ~0.45 ft^3 |
| 80 lb | ~45 bags | ~0.60 ft^3 |
Values are planning approximations. Actual yield varies by mix design, aggregate, and manufacturer label instructions.
Results
Planning multiple pours? Use the full project estimator →
Material Cost Estimate
Prices vary by market; use local quotes.
Typical Concrete Slab Cost
For planning, many residential slab projects are commonly discussed in a broad installed range of roughly $6 to $15+ per square foot, with some jobs landing outside that band based on scope and local conditions. This should be treated as directional only, not a fixed quote. Concrete pricing varies by market, and the same slab size can price very differently depending on site access, labor demand, finish level, and dispatch logistics on pour day.
The biggest cost drivers are usually slab thickness and mix strength (PSI), then reinforcement requirements and placement complexity. A thicker slab or higher PSI mix increases material volume and can raise ready-mix rates. Rebar or wire mesh adds both material and labor. If truck access is limited and a pump is needed, that can add a meaningful line item. Site prep also moves totals: grading, base compaction, removal of old concrete, and drainage corrections all affect labor hours before the pour even starts. Finish choices can further separate bids, especially when you move from a basic broom finish to decorative edges, stamping, or tighter tolerance work.
Use this calculator to size volume first, then translate that into a realistic budget range with local quotes.
- Measure slab length, width, and target thickness; add a practical waste factor.
- Choose the PSI and reinforcement level that match load and durability needs.
- Estimate site prep, access constraints, and pump requirements before bid comparison.
- Separate base concrete pricing from finish upgrades so line items are comparable.
- Request multiple local quotes and validate what is included vs. billed separately.
For fee structure details and mix-level pricing context, see the pricing breakdown.
Assumptions
- Standard material density assumptions are used for weight and bag yield estimates.
- Industry standard conversion formulas are used for cubic feet, cubic yards, and metric volumes.
- Waste factor explains extra volume for spillage, uneven forms, and over-excavation.
Next Steps: Concrete Project Workflow
Example
A 10 ft × 12 ft slab at 4 inches thick with 10% waste is 1.63 yd³ of concrete. Adjust thickness and waste based on your project.
Example 2: Concrete Garage Slab
Project: 24 ft x 24 ft two-car garage slab at 6 inches thick
- Length: 24 ft
- Width: 24 ft
- Thickness: 6 inches
- Waste: 10%
- Base volume: 12.80 yd^3
- With 10% waste: 14.08 yd^3
- Ready-mix order: Round up to 14.5 yards
Why 6 inches? Garage slabs must support vehicle weight. A 6-inch slab with 3,500-4,000 PSI concrete is standard for residential garages.
Example 3: Backyard Patio Slab
Project: 12 ft x 16 ft patio at 4 inches thick
- Length: 12 ft
- Width: 16 ft
- Thickness: 4 inches
- Waste: 10%
- Base volume: 2.37 yd^3
- With waste: 2.61 yd^3
- Ready-mix order: Round up to 2.75 yards
Why 4 inches? Patios typically require 4 inches minimum for foot traffic and light furniture loads.
How to Calculate Concrete for a Slab (Formula)
Formula: (Length ft x Width ft x Thickness in / 12) / 27 = cubic yards
Example: A 10 ft x 12 ft slab at 4 inches thick is (10 x 12 x 4 / 12) = 40 ft^3. Then 40 / 27 = 1.48 yd^3 before waste.
Common Concrete Slab Mistakes to Avoid
- Pouring too thin - 4 inches is minimum for most slabs. Thinner slabs crack prematurely.
- Skipping gravel base - 4-6 inches of compacted gravel prevents settling and cracking.
- Underestimating waste - Always add at least 10% to avoid running short mid-pour.
- No control joints - Cut joints every 8-12 feet to control cracking.
- Using bagged concrete for large pours - Over 2 cubic yards should use ready-mix delivery.
Ready-Mix vs Bagged Concrete for Slabs
| Project Size | Best Option | Why |
|---|---|---|
| Under 1 yd^3 | Bagged concrete | Easier for small DIY pours |
| 1-2 yd^3 | Either | Depends on labor availability |
| Over 2 yd^3 | Ready-mix delivery | Faster, consistent quality, less labor |
For most slabs larger than a small patio, ready-mix delivery is more economical and significantly reduces labor time.
Related Concrete Calculators
Planning a more specialized concrete project? Use one of these project-specific calculators:
- Concrete Column Calculator
- Concrete Curb and Gutter Calculator
- Concrete Curing Time Calculator
- Concrete Patio Calculator
- Concrete Steps Calculator
- Concrete Retaining Wall Calculator
- Concrete Beam Calculator
- Concrete Ramp Calculator
- Concrete Stoop Calculator
- Concrete Countertop Calculator
For mix design and lifecycle planning, compare this slab takeoff with the Concrete Thickness by Project guide and the Concrete Patio Cost guide.
Concrete Slab Calculator FAQs
How many yards of concrete do I need?
The total yards you need depends on slab length, width, thickness, and waste percentage. Multiply length by width by thickness in feet to get cubic feet, then divide by 27 for cubic yards. The calculator already applies your waste setting so your result is closer to an order-ready number.
How do I calculate slab volume?
Slab volume is calculated as length × width × thickness. Use feet for all dimensions to get cubic feet, then divide by 27 to convert to cubic yards. If thickness starts in inches, divide by 12 first so units stay consistent.
How thick should a concrete slab be?
A common baseline is 4 inches for light-duty slabs. Driveways, garage slabs, and heavy loads often require 5 to 6 inches or more. Local code and soil conditions can change thickness requirements, so confirm before finalizing material orders.
How many 80 lb bags of concrete equal one yard?
One cubic yard is roughly 45 bags of 80 lb concrete mix. Exact yield varies by manufacturer and mix design, so always check the bag label. For larger pours, ready-mix is usually faster and more consistent than bag mixing.
How much extra concrete should I order?
Most slab projects use about 5 to 10 percent extra concrete. Simple rectangular pours can often stay near the low end, while irregular forms and thickened edges usually need more. If access is difficult or timing is tight, a slightly larger buffer reduces the risk of coming up short.
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- Concrete Slab Thickness Guide
- Concrete Thickness by Project Type (Quick Chart)
- Concrete Slab Reinforcement Guide (Rebar vs Wire Mesh)
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