Concrete Slab Cost Calculator
Whether you're pouring a backyard patio or a driveway foundation, knowing the exact volume of concrete required prevents costly over-ordering and project delays. Enter your slab dimensions and material price to get an accurate cost breakdown in seconds.
Quick Reference
Concrete Thickness Guide
Choosing the right thickness is critical – too thin and the slab cracks under load, too thick and you're wasting money. Here's what to use for different applications:
| Project Type | Recommended Thickness | Concrete per 100 sq ft | Cost at $150/yd³ |
|---|---|---|---|
| Sidewalks | 4 inches | 1.23 yd³ | $184.50 |
| Patios | 4 inches | 1.23 yd³ | $184.50 |
| Driveways | 6 inches | 1.85 yd³ | $277.50 |
| Garage Floors | 4-6 inches | 1.23 - 1.85 yd³ | $184.50 - $277.50 |
| Foundations | 8-12 inches | 2.47 - 3.70 yd³ | $370.50 - $555.00 |
These thicknesses assume standard residential loads. For commercial or industrial applications, consult a structural engineer – you may need reinforced concrete with rebar or wire mesh.
Concrete Bag Coverage Chart
For small projects, bagged concrete may be more practical than ready-mix delivery. Here's how different bag sizes translate to coverage:
| Bag Size | Cubic Feet per Bag | Bags per Cubic Yard | Coverage @ 4" Thick | Typical Price |
|---|---|---|---|---|
| 40 lb Bag | 0.30 ft³ | 90 bags | 0.9 sq ft | $3.50-$5.00 |
| 60 lb Bag | 0.45 ft³ | 60 bags | 1.35 sq ft | $4.00-$5.50 |
| 80 lb Bag | 0.60 ft³ | 45 bags | 1.8 sq ft | $4.50-$6.50 |
Quick rule: You need about 45 eighty-pound bags to make one cubic yard of concrete. For a 100 sq ft patio at 4 inches thick, that's roughly 56 eighty-pound bags – a lot of mixing by hand.
Ready-Mix vs Bagged Concrete
Choosing between ready-mix delivery and bagged concrete depends on your project size, budget, and how much labor you're willing to do:
| Factor | Ready-Mix Delivery | Bagged Concrete |
|---|---|---|
| Best for | Projects over 1 cubic yard | Small patches, posts, under 1 yd³ |
| Cost per yd³ | $125-$175 (including delivery) | $200-$300 (45 bags – $5) |
| Labor | Minimal – truck pours directly | Heavy – mix each bag by hand or mixer |
| Quality | Consistent factory mix | Varies with mixing technique |
| Delivery | Needs truck access to site | Carry bags to the work area |
| Minimum order | Typically 1-3 yd³ | Buy exactly what you need |
Rule of thumb: If your project is over 1 cubic yard, ready-mix is almost always cheaper and better quality. For small repairs and fence post footings, bagged concrete is more practical.
Concrete Cost Guide
The total cost of a concrete project includes more than just the concrete itself. Here's a breakdown of what to budget for:
| Cost Component | Typical Range | Notes |
|---|---|---|
| Concrete Material | $125-$175 per yd³ | Ready-mix delivered, 2026 prices |
| Delivery Fee | $50-$150 | Often included for orders over 2 yd³ |
| Site Preparation | $1-$3 per sq ft | Grading, compacting, formwork |
| Labor | $2-$4 per sq ft | Pouring, leveling, finishing |
| Finishing | $1-$5 per sq ft | Brushed finish $1, stamped $5+ |
| Rebar/Wire Mesh | $0.50-$1.50 per sq ft | Required for driveways and slabs over 4" |
Total budget estimate: For a basic 4-inch patio, expect $8-$15 per square foot all-in. For a 6-inch driveway with rebar and finishing, budget $12-$20 per square foot.
Concrete Curing Timeline
Concrete doesn't dry – it cures through a chemical reaction called hydration. Understanding the timeline helps you plan when to use your new slab:
| Time After Pouring | Strength Achieved | What You Can Do |
|---|---|---|
| 24 Hours | ~15% of design strength | Forms can be removed. Keep surface damp. No foot traffic. |
| 3 Days | ~40% of design strength | Light foot traffic OK. Continue curing (keep moist). |
| 7 Days | ~70% of design strength | Vehicle traffic OK for driveways. Most construction loads. |
| 28 Days | 100% design strength | Full use. Concrete has reached its rated strength. |
Curing tip: Keep the concrete moist for the first 7 days by covering it with plastic sheeting or spraying it with water several times a day. Proper curing can increase final strength by 20-30%.
Worked Example
Let's calculate the cost of a 20 ft × 12 ft patio with 4 inches of concrete at $150 per cubic yard:
Step 1 – Area: 20 × 12 = 240 square feet.
Step 2 – Volume in cubic feet: 240 × (4 ÷ 12) = 240 × 0.333 = 80 ft³.
Step 3 – Volume in cubic yards: 80 ÷ 27 = 2.96 yd³.
Step 4 – Order volume with 10% waste: 2.96 × 1.10 = 3.26 yd³.
Step 5 – Total cost: 3.26 × $150 = $489.00.
Step 6 – Cost per square foot: $489 ÷ 240 = $2.04/ft².
This example shows a basic patio – a 4-inch slab at $150/yd³. If you needed a 6-inch driveway slab instead, the volume would be 120 ft³ (4.44 yd³) costing $732.60 with waste. The thickness choice is the single biggest cost driver for concrete slabs.
How to Use This Calculator
Step 1: Enter the length and width of your slab in feet. Measure the actual area the concrete will cover, including any extensions beyond footings.
Step 2: Set the slab thickness in inches. Use 4 inches for patios and walkways, 6 inches for driveways, and 8-12 inches for foundations and heavy-duty slabs.
Step 3: Enter the price per cubic yard. In 2026, ready-mix concrete costs $125-$175 per cubic yard, with $150 being a solid average for budgeting.
Step 4: Set the waste factor. The calculator defaults to 10%, which accounts for spillage, uneven ground, and pouring waste. For simple flat slabs on level ground, 5% is often sufficient.
Step 5: Click "Calculate" to see your results – volume in cubic feet and yards, order amount with waste, total cost, and cost per square foot.
Concrete Calculator Formula
The calculator uses a three-step formula to determine your slab volume and cost:
- Volume (ft³) = Length (ft) × Width (ft) × (Thickness in inches ÷ 12)
- Volume (yd³) = Volume (ft³) ÷ 27
- Order Volume = Volume (yd³) × (1 + Waste Factor ÷ 100)
- Total Cost = Order Volume × Price per Cubic Yard
- Cost per Sq Ft = Total Cost ÷ (Length × Width)
The thickness conversion (÷ 12) converts inches to feet so all dimensions are in the same unit. Dividing by 27 converts cubic feet to cubic yards, which is how ready-mix concrete is sold. The waste factor ensures you order enough to account for spillage and uneven pouring without running short.
Tips & Common Mistakes
✓ Do This
- Check local building codes – some areas require permits for slabs over a certain size.
- Call 811 before digging – have underground utilities marked to avoid hitting gas, water, or electrical lines.
- Compact the subgrade – loose soil settles over time, causing cracks. Compact to 95%+ Proctor density.
- Add gravel base – 4-6 inches of compacted gravel improves drainage and reduces cracking.
- Build strong forms – use 2×4 or 2×6 lumber secured with stakes.
- Plan your pour path – know where the truck will position and how concrete will flow.
- Have finishing tools ready – bull float, trowel, edger, and broom on-site before the truck arrives.
✗ Avoid This
- Skipping the gravel base: Pouring directly on soil leads to uneven settling, cracks, and slab failure.
- Not ordering enough: Running short mid-pour creates cold joints. Order 10% more than calculated.
- Ignoring weather: Don't pour in extreme heat (above 90°F) or freezing temps (below 35°F).
- Over-working the surface: Excessive troweling creates a weak layer that scales and peels.
- Not curing properly: Concrete that dries too fast cracks. Keep moist for at least 7 days.
- Ignoring control joints: Cut control joints every 1.5× the slab thickness to control cracks.
Common Slab Dimensions & Pre-Calculated Volumes
These are the most common residential slab sizes. Use this table as a quick reference without running the calculator.
| Project Type | Typical Size | Thickness | Volume (cu yd) | @ $150/cu yd |
|---|---|---|---|---|
| Small Patio | 10 × 10 ft | 4 in | 1.23 | $185 |
| Large Patio | 20 × 16 ft | 4 in | 3.95 | $593 |
| Single-Car Driveway | 10 × 20 ft | 6 in | 3.70 | $556 |
| Double-Car Driveway | 20 × 20 ft | 6 in | 7.41 | $1,111 |
| Shed Foundation | 10 × 12 ft | 4 in | 1.48 | $222 |
| Garage Slab | 20 × 24 ft | 6 in | 8.89 | $1,333 |
| Walkway (3 ft wide) | 3 × 20 ft | 4 in | 0.89 | $133 |
| Pool Deck (surround) | 15 × 15 ft (surround) | 4 in | 2.78 | $417 |
Volumes include a 10% waste factor. Prices reflect 2026 national averages — actual cost varies by region and mix design.
DIY vs. Hiring a Contractor
Concrete work is one of the more demanding DIY projects. Here's an honest breakdown of when each makes sense, based on industry data:
| Factor | DIY | Hire a Contractor |
|---|---|---|
| Labor cost | $0 (your time) | $2–$8 per sq ft [1] |
| Total savings | 50–60% on labor portion [2] | N/A |
| Best for | Small projects under 1 cu yd (~45 bags of 80lb) | Any project over 1 cu yd, driveways, foundations |
| Quality | Varies with experience — finishing is skill-dependent | Consistent, professional finish |
| Equipment needed | Concrete mixer ($60–$120 rental), floats, trowels, forms | All provided by contractor |
| Time | 2–3× longer than pros for same area | Crew of 3–4 can pour 400 sq ft in 4–6 hours |
| Risk | Cold joints, poor finishing, cracking if not cured properly | Low — contractor carries insurance and warranty |
| Permits | Still required in most areas — you must pull them yourself | Contractor typically handles permits |
When DIY Makes Sense
- Volume under 1 cubic yard — about 45 eighty-pound bags. This covers small patios, shed pads, and fence post footings.
- You have 3+ helpers — concrete sets fast. You need enough people to place, level, and finish before it hardens.
- Finish quality is secondary — a shed pad or utility slab doesn't need a polished finish.
- Budget is the primary constraint — DIY saves $2–$8/sq ft on labor, which adds up fast on larger areas.
When to Hire a Pro
- Volume exceeds 1 cubic yard — ready-mix delivery is more practical and often cheaper than mixing 45+ bags by hand.
- Project is structural — driveways, garage floors, and foundations require proper reinforcement, grading, and finishing.
- Surface finish matters — decorative finishes (stamped, exposed aggregate, polished) require specialized tools and experience.
- Local code requires a licensed contractor — some jurisdictions require licensed contractors for structural work.
Sources: [1] BLS Occupational Employment Statistics 2024 (concrete finishers $20–$35/hr). [2] HomeAdvisor 2026 cost guide — labor typically represents 50–60% of total installed cost for residential flatwork.
Frequently Asked Questions
Enter your slab dimensions (length, width, thickness) and price per cubic yard. The calculator computes volume in cubic feet and yards, applies a waste factor, and multiplies by your price to get the total cost.
For patios and walkways, 4 inches is standard. Driveways need 6 inches to handle vehicle weight. Garage slabs use 4-6 inches. Foundations and heavy-duty slabs require 8-12 inches.
In 2026, ready-mix concrete costs $125-$175 per cubic yard, with $150 being a solid average. Price varies by region, mix design, and order volume.
Order 5-10% more than your calculated volume to account for spillage, uneven ground, and waste during pouring. The calculator includes a waste factor field for this.
Material price, slab thickness, labor rates, site preparation, finishing options (stamped, stained, brushed), rebar reinforcement, and your geographic location all impact final cost.
For small projects under 1 cubic yard, bagged concrete ($4-$6 per 80 lb bag) can be cheaper. For larger slabs, ready-mix delivery is more economical and ensures consistent quality.
Concrete sets in 24-48 hours, reaches 70% strength at 7 days, and achieves full design strength at 28 days. Wait at least 7 days before driving on new driveways.
For slabs under 4 inches thick, wire mesh is usually sufficient. For driveways, slabs over 4 inches, or areas with heavy loads, rebar provides crucial structural reinforcement and crack prevention.