Footprint
Enter or confirm the 30 by 40 foot footprint. Its calculated area is 1,200 square feet.
Concrete slab estimate
30x40 Concrete Slab Cost
A 30x40 slab covers 1,200 sq ft and at 4 inches with 10% added needs about 16.30 cubic yards or 734 80 lb bags. The national installed baseline is $7,200–$14,400.
30x40 concrete slab cost calculator
Adjust dimensions, thickness, allowance, or metro area. The installed range uses the national $6–$12 per-square-foot baseline with the existing metro model.
Baseline: 1,200 sq ft at 4 inches, with 10% added allowance. Metro adjustments use the site's existing BLS wage model.
How to use this 30x40 calculator
Thickness
Select 4, 5, or 6 inches to update the concrete volume and bag estimate for this same footprint.
Allowance
The baseline adds 10% to the geometric volume for planning. Actual ordering quantities depend on the measured site and placement conditions.
Metro
Metro comparisons are general estimates using the site's existing labor adjustment. They are not local supplier quotes.
30x40 slab calculation formula
Volume
30 × 40 = 1,200 square feet. Area × (4 ÷ 12) × 1.1 = 440.00 cubic feet including allowance.
Cubic yards and bags
440.00 ÷ 27 = 16.30 cubic yards. Dividing the same volume by 0.6 cubic feet per bag and rounding up gives 734 bags.
Price
1,200 square feet × $6–$12 per square foot gives the installed baseline of $7,200–$14,400.
Concrete slab prices by size
Compare the 4-inch national baseline across published footprints.
| Slab size | Area | Concrete | 80 lb bags | Installed cost | Price basis |
|---|---|---|---|---|---|
| 10x10 concrete slab cost | 100 sq ft Estimated | 1.36 yd³ Estimated | 62 Estimated | $600–$1,200 Estimated | National installed baseline Estimated |
| 12x12 concrete slab cost | 144 sq ft Estimated | 1.96 yd³ Estimated | 88 Estimated | $860–$1,730 Estimated | National installed baseline Estimated |
| 20x20 concrete slab cost | 400 sq ft Estimated | 5.43 yd³ Estimated | 245 Estimated | $2,400–$4,800 Estimated | National installed baseline Estimated |
| 20x30 concrete slab cost | 600 sq ft Estimated | 8.15 yd³ Estimated | 367 Estimated | $3,600–$7,200 Estimated | National installed baseline Estimated |
| 30x30 concrete slab cost | 900 sq ft Estimated | 12.22 yd³ Estimated | 550 Estimated | $5,400–$10,800 Estimated | National installed baseline Estimated |
| 30x40 concrete slab cost | 1,200 sq ft Estimated | 16.30 yd³ Estimated | 734 Estimated | $7,200–$14,400 Estimated | National installed baseline Estimated |
| 30x50 concrete slab cost | 1,500 sq ft Estimated | 20.37 yd³ Estimated | 917 Estimated | $9,000–$18,000 Estimated | National installed baseline Estimated |
| 40x60 concrete slab cost | 2,400 sq ft Estimated | 32.59 yd³ Estimated | 1,467 Estimated | $14,400–$28,800 Estimated | National installed baseline Estimated |
| 60x80 concrete slab cost | 4,800 sq ft Estimated | 65.19 yd³ Estimated | 2,934 Estimated | $28,800–$57,600 Estimated | National installed baseline Estimated |
30x40 slab thickness by use
Patio
Use the 4-inch result as the baseline quantity for a 30x40 patio footprint.
Driveway
Compare the same footprint at 5 inches: 20.37 cubic yards and 917 bags.
Load-bearing foundation
A 6-inch quantity model gives 24.44 cubic yards and 1,100 bags. Structural design and required thickness depend on the project.
Concrete quantity and material cost by thickness
| Thickness | Cubic yards | 80 lb bags | Installed baseline |
|---|---|---|---|
| 4 in | 16.30 yd³ | 734 | $7,200–$14,400 |
| 5 in | 20.37 yd³ | 917 | $7,200–$14,400 |
| 6 in | 24.44 yd³ | 1,100 | $7,200–$14,400 |
Installed prices in this table use a single national $6–$12/sq ft baseline and do not change by thickness. See how price shifts by slab depth →
30x40 slab cost by metro area
Metro estimates adjust the labor share with BLS May 2025 construction and extraction wages. They do not represent ZIP-code or supplier quotes.
| Metro area | BLS construction wage | Modeled $/sq ft | 30x40 installed total | Level |
|---|---|---|---|---|
| United States — national average concrete cost | $31.42/hr Verified | $6.00–$12.00 Estimated | $7,200–$14,400 Estimated | BLS May 2025 model |
| Dallas–Fort Worth–Arlington concrete cost | $27.03/hr Verified | $5.62–$11.25 Estimated | $6,740–$13,500 Estimated | BLS May 2025 model |
| Chicago–Naperville–Elgin concrete cost | $40.87/hr Verified | $6.81–$13.62 Estimated | $8,170–$16,340 Estimated | BLS May 2025 model |
| Seattle–Tacoma–Bellevue concrete cost | $42.11/hr Verified | $6.92–$13.84 Estimated | $8,300–$16,610 Estimated | BLS May 2025 model |
| Atlanta–Sandy Springs–Roswell concrete cost | $28.26/hr Verified | $5.73–$11.46 Estimated | $6,880–$13,750 Estimated | BLS May 2025 model |
Sources: BLS OEWS metro data, May 2025, and HomeGuide's national installed range of $6–$12/sq ft, February 3, 2026.
DIY material baseline vs. installed price
DIY quantity baseline
The 30x40 footprint requires 16.30 cubic yards or 734 bags at the 4-inch baseline. This quantity does not price delivery, labor, forms, or site preparation.
Installed price
The national installed range is $7,200–$14,400. Compare scope details with a contractor before treating a quote as equivalent to this planning estimate.
Items that can change a 30x40 quote
Site preparation
Excavation, removal, grading, and base preparation can change the work covered by a quote.
Reinforcement
Reinforcement details vary by design and project scope; check which materials and placement are included.
Access and placement
Truck access, pumping, and placement distance can affect how the work is performed.
Finish and joints
Surface finish, joint layout, cleanup, and exclusions should be compared across written bids.
30x40 concrete slab cost FAQ
How much concrete does a 30x40 slab need?
At 4 inches with the 10% allowance, it needs about 16.30 cubic yards or 734 80 lb bags.
How much does a 30x40 slab cost?
The national installed baseline is $7,200–$14,400 for 1,200 square feet.
How many square feet is a 30x40 slab?
30 feet × 40 feet equals 1,200 square feet.
How many 80 lb bags are needed?
The 4-inch baseline estimates 734 bags after adding the planning allowance and rounding up.
How does thickness change the quantity?
At 5 inches the quantity is 20.37 cubic yards; at 6 inches it is 24.44 cubic yards for the same footprint.
Does this estimate equal a contractor quote?
No. The $7,200–$14,400 range is a national installed baseline; local scope, site conditions, and written exclusions can change a quote.
Got a quote? Send it over—we’ll help you check whether it looks reasonable.
Compare its total with the 30x40 planning baseline.
Use the related quote checklist to compare written scope.