Concrete Slab Cost Calculator
Calculate concrete volume, bags, ready-mix yardage, and full project cost for slabs, garage floors, and patios.
Concrete Slab Cost Calculator
Volume, bags, supplier ordering, and complete project cost breakdown
ACI recommendation: +10% for slabs
Net pour: 2.96 yd³ · 240 sq ft · 4" thick
Rounded to 0.25 yd increment · min 1 yd order
How to Calculate Concrete Slab Cost
Concrete slab cost estimation starts with accurate volume calculation, then layers on material, labor, and site preparation costs:
324 = 27 cu ft/yd × 12 in/ft. Always add 8–10% waste.
ACI recommends 10% over-pour for form deflection and subgrade variation.
Plants batch in 0.25-yd increments; minimum order is typically 1 yard.
Include all line items: concrete, labor, delivery, and finishing.
Worked Example: 12×20 Slab at 4" Thickness
- Surface area: 12 ft × 20 ft = 240 sq ft
- Net volume: (240 × 4) ÷ 324 = 2.963 cu yds
- +10% waste: 2.963 × 1.10 = 3.259 cu yds
- Supplier bills: ⌈3.259 ÷ 0.25⌉ × 0.25 = 3.50 cu yds
- At $150/yd³ + $75 delivery: 3.50 × $150 + $75 = $600
Ready-Mix vs. Bagged Concrete Comparison
The break-even point between bagged and ready-mix concrete is typically around 1.5 cubic yards (68 eighty-pound bags):
| Volume Required | 80-lb Bags | Bag Weight | Bagged Cost (~$6/bag) | Ready-Mix Cost (~$150/yd) | Recommended |
|---|---|---|---|---|---|
| 0.5 yd³ | 23 bags | 1,840 lbs | $138 | $275 (min fee) | Bagged |
| 1.0 yd³ | 45 bags | 3,600 lbs | $270 | $300 (short-load) | Either |
| 2.0 yd³ | 90 bags | 7,200 lbs | $540 | $375 | Ready-Mix |
| 6.0 yd³ (garage) | 270 bags | 21,600 lbs | $1,620 | $975 | Ready-Mix |
What's Included in Concrete Slab Cost?
A thorough concrete slab budget covers every phase from site prep to surface finishing:
- ✓Excavation: Removing soil to the required depth, typically $1–$3/sq ft.
- ✓Gravel Base: 4"–6" compacted sub-base for drainage, $0.50–$1.50/sq ft.
- ✓Vapor Barrier: 6-mil poly sheeting to prevent moisture migration, $0.10–$0.25/sq ft.
- ✓Formwork: 2×4 or 2×6 lumber frames at $1–$3/lin ft of perimeter.
- ✓Rebar / Wire Mesh: Structural reinforcement, $0.30–$1.00/sq ft installed.
- ✓Concrete Material: Ready-mix at $130–$175/yd³ plus delivery fee.
- ✓Pump Fee: Concrete pump truck when truck can't reach the pour, $500–$1,500 flat.
- ✓Labor — Pour: Placing, screeding, and floating, $1–$3/sq ft.
- ✓Surface Finish: Broom finish ($0.50–$1), trowel ($1–$2), or stamped ($6–$15/sq ft).
- ✓Short-Load Fee: Surcharge for orders under 4–5 yards, typically $120–$250.
- ✓Tax & Contingency: Sales tax on materials plus 10–15% contingency reserve.
- ✓Permit: Building permit for slabs >200 sq ft, $50–$300 depending on jurisdiction.
Concrete Slab Cost Calculator FAQs
How much does a concrete slab cost per square foot?
A residential concrete slab typically costs $4 to $8 per square foot for basic concrete material and placement (ready-mix only). With labor, formwork, gravel base, rebar, and finishing, full project costs range from $6 to $12 per square foot. Decorative or stamped finishes can reach $15 to $25 per square foot. Use this calculator to build a line-item budget for your specific project.
How many cubic yards for a 12x20 concrete slab?
A 12 ft × 20 ft slab (240 sq ft) at 4 inches thick requires: (240 × 4) ÷ 324 = 2.96 cubic yards net. Adding the standard 10% over-pour margin gives 3.26 cubic yards. The ready-mix supplier will bill 3.50 cubic yards (rounded up to the nearest 0.25-yard increment).
What is included in a concrete slab cost estimate?
A complete concrete slab cost estimate includes: (1) Excavation and subgrade prep, (2) Compacted gravel base, (3) Vapor barrier / poly sheeting, (4) Formwork lumber and stakes, (5) Rebar or wire mesh reinforcement, (6) Ready-mix concrete material, (7) Concrete pump fee if access is limited, (8) Concrete delivery fee, (9) Labor for placing, screeding, and floating, (10) Surface finishing (broom, trowel, or stamped), and (11) Tax and contingency. This calculator provides a line-by-line estimate for all categories.
Do I need a permit for a concrete slab?
Permit requirements vary by municipality. Most jurisdictions require a building permit for concrete slabs larger than 200–400 sq ft, any slab attached to a structure, or slabs with footings. Patio slabs under a certain threshold (commonly 200 sq ft) are often exempt. Always check with your local building department before pouring — permits typically cost $50 to $300 and require a site inspection.
How thick should a concrete slab be for a garage?
Residential garage slabs should be a minimum of 4 inches thick (ACI 360 recommendation for light vehicle traffic). For heavier vehicles, workshops, or areas subject to point loads from car lifts or storage racking, 5 to 6 inches is recommended. Use 4,000 PSI concrete with 5–7% air entrainment in freeze-thaw climates, and include a rebar grid (#4 rebar at 24" on center) or fiber reinforcement to control cracking.
What is a short-load fee for ready-mix concrete?
Ready-mix suppliers charge a short-load (or under-load) fee when you order less than their minimum full-load threshold, typically 4 to 5 cubic yards. The fee compensates for the fixed operating cost of dispatching a truck — typically $120 to $250 depending on the plant and distance. For projects under 2 cubic yards, bagged concrete often beats ready-mix even after accounting for the short-load surcharge.
How much does concrete cost per cubic yard?
Ready-mix concrete prices vary by region, mix design, and market conditions. The national average for standard 3,000–4,000 PSI residential concrete ranges from $130 to $175 per cubic yard, plus $75–$150 delivery fee. High-strength (5,000+ PSI), fiber-reinforced, or color-added mixes cost $155–$220 per cubic yard. Always get at least 3 local quotes — regional variation can exceed $40–$60 per yard.
Should I hire a contractor or pour concrete myself?
DIY concrete is feasible for small slabs under 1.5 cubic yards (patio squares, steps, pads). For larger slabs, the professional quality difference in screeding, finishing, and cure control is significant. Professionals also carry liability insurance if the slab fails. As a rough guide: if the project exceeds 20 bags of bagged concrete or 1.5 cubic yards of ready-mix, the labor savings from professional contractors typically outweigh the DIY cost savings, especially when factoring in tool rental and risk.
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