1. Find cubic feet
Length ft × width ft × (thickness in ÷ 12)For 20×20×4 in, net volume is 133.33 ft³Estimated. With the default allowance, it becomes 146.67 ft³Estimated.
U.S. concrete quantity and installed cost estimator
Concrete Slab Cost Calculator
Use this concrete slab cost calculator to price any slab by size, thickness, and U.S. metro—a 20×20 ft slab at 4 inches thick needs about 5.43 cubic yardsEstimated, including a 10% waste factor, and typically costs $2,400–$4,800 installedVerified.
Installed price source: HomeGuide concrete slab cost research, February 3, 2026. Quantity is calculated from the dimensions shown. Compare delivered rates with the concrete cost per yard estimator.
Estimate concrete quantity and installed price
Change any field and all four results update together. Calculations stay in your browser.
Concrete volume
5.43 yd³
Includes selected waste Estimated
80 lb concrete bags
245 bags
Rounded up to whole bags Estimated
Installed project cost
$2,400–$4,800
U.S. national benchmark Estimated
Installed price per sq ft
$6.00–$12.00
Location and thickness adjusted Estimated
Price basis: HomeGuide, February 3, 2026 ($6–$12/sq ft installedVerified). Metro adjustment: BLS OEWS, May 2025. Bag yield: QUIKRETE Concrete Mix data sheet, revised October 2022.
How to use the calculator
01
Enter the footprint
Use the slab's measured length and width in feet. The calculator multiplies them to obtain square footage.
02
Set the thickness
Enter thickness in inches. The default is 4 inches, and the thickness directly changes concrete volume.
03
Choose the allowance
The default 10% waste factor is applied after the net volume is calculated. Change it to match the allowance in your estimate.
04
Select a metro area
Choose the nearest listed metro or keep the national view. Location changes only the estimated labor share of the price range.
Concrete calculator formula
The quantity calculation follows a traceable path: cubic feet, then cubic yards, then the applicable unit-price basis.
2. Convert to cubic yards
Cubic feet ÷ 27 = cubic yardsThe default example is 146.67 ÷ 27 = 5.43 yd³Estimated. Bag count divides the same cubic feet by 0.60 ft³ per 80 lb bagVerified and rounds up.
3. Apply the unit price
Quantity × unit price = costMaterial-only budgeting can multiply cubic yards by a local $/yd³ quote; see current concrete cost per yard rates by metro. This page's installed total instead starts with the verified national $6–$12/sq ftVerified range and adjusts it for thickness and metro labor wages.
Why the installed result is not simply ready-mix price. HomeGuide separates a concrete slab's cost into a $3–$7/sq ft material shareVerified and a $3–$5/sq ft labor shareVerified, dated February 3, 2026. The calculator uses the midpoint split—55% material and 45% laborEstimated—to adjust thickness and metro wages without claiming supplier-quote precision.
For a material-only comparison, HomeGuide reports $119–$147 per cubic yard for ready-mix concrete in its concrete pricing guide, including delivery up to 20 miles. The page is dated January 6, 2026; short-load fees may apply.
Concrete slab cost by size
Quantities assume a 4-inch thickness and 10% waste factor. Installed prices use the national baseline before metro adjustment. Use this slab cost calculator to compare concrete slab cost by size before applying your local metro adjustment.
| Slab size | Area | Concrete | 80 lb bags | Installed cost | Price level |
|---|---|---|---|---|---|
| 12×12 concrete slab cost | 144 sq ft Estimated | 1.96 yd³ Estimated | 88 Estimated | $860–$1,730 Estimated | HomeGuide $6–$12/sq ft, Feb. 3, 2026 |
| 20×20 concrete slab cost | 400 sq ft Estimated | 5.43 yd³ Estimated | 245 Estimated | $2,400–$4,800 Verified | HomeGuide, Feb. 3, 2026 |
| 30×50 concrete slab cost | 1,500 sq ft Estimated | 20.37 yd³ Estimated | 917 Estimated | $9,000–$18,000 Estimated | HomeGuide $6–$12/sq ft, Feb. 3, 2026 |
| 40×60 concrete slab cost | 2,400 sq ft Estimated | 32.59 yd³ Estimated | 1,467 Estimated | $14,400–$28,800 Estimated | HomeGuide $6–$12/sq ft, Feb. 3, 2026 |
| 60×80 concrete slab cost | 4,800 sq ft Estimated | 65.19 yd³ Estimated | 2,934 Estimated | $28,800–$57,600 Estimated | HomeGuide $6–$12/sq ft, Feb. 3, 2026 |
Source: HomeGuide, February 3, 2026, for the national installed rate and the rows explicitly marked Verified. Estimated rows multiply area by the same published rate. Volume and bags are formula estimates using QUIKRETE's October 2022 yield.
A 20×20 slab at 4 inches thick needs about 5.43 cubic yardsEstimated, and at the verified U.S. average it costs about $2,400–$4,800 installedVerified. Price source: HomeGuide, February 3, 2026.
Concrete cost by U.S. metro area
The 20 × 20 ft, 4-inch scenario changes only the labor share using BLS May 2025 construction and extraction wages.
| Metro area | BLS wage | Modeled $/sq ft | Installed total |
|---|---|---|---|
| Dallas–Fort Worth–Arlington | $27.03/hr Verified | $5.62–$11.25 Estimated | $2,250–$4,500 Estimated |
| Chicago–Naperville–Elgin | $40.87/hr Verified | $6.81–$13.62 Estimated | $2,720–$5,450 Estimated |
| Seattle–Tacoma–Bellevue | $42.11/hr Verified | $6.92–$13.84 Estimated | $2,770–$5,530 Estimated |
| Atlanta–Sandy Springs–Roswell | $28.26/hr Verified | $5.73–$11.46 Estimated | $2,290–$4,580 Estimated |
Sources: BLS OEWS metro data, May 2025, and HomeGuide's $6–$12/sq ftVerified national range, February 3, 2026. These are metro-level estimates, not ZIP-code prices.
Concrete needed by slab thickness
Use this table to compare the amount required for each 100 sq ft of slab area, including the default 10% allowance. Because volume increases with depth, concrete slab cost generally rises as thickness changes from 4 to 5 or 6 inches.
| Thickness | Net cubic feet | With 10% allowance | Cubic yards | 80 lb bags |
|---|---|---|---|---|
| 4 inches | 33.33 ft³ Estimated | 36.67 ft³ Estimated | 1.36 yd³ Estimated | 62 Estimated |
| 5 inches | 41.67 ft³ Estimated | 45.83 ft³ Estimated | 1.70 yd³ Estimated | 77 Estimated |
| 6 inches | 50.00 ft³ Estimated | 55.00 ft³ Estimated | 2.04 yd³ Estimated | 92 Estimated |
Bag counts use 0.60 ft³ per 80 lb bagVerified, QUIKRETE Concrete Mix technical data, revised October 2022. All calculated quantities are marked Estimated because actual packaged yield can vary.
DIY material cost vs. hiring a contractor
The comparison separates ready-mix concrete from the broader installed benchmark. The scopes are not equivalent.
DIY: ready-mix material only
$650–$870 EstimatedThe default 5.43 yd³ is multiplied by HomeGuide's $120–$160/yd³Verified range dated April 3, 2026. Forms, base, reinforcement, tools, delivery modifiers, finishing, and labor are outside this card. Compare the current cost per cubic yard with your local supplier quote.
Contractor: installed benchmark
$2,400–$4,800 VerifiedThe national baseline is the 400 sq ft footprint multiplied by HomeGuide's $6–$12/sq ft installedVerified range dated February 3, 2026. An actual bid may define its included work differently.
Scope gap: $1,530–$4,150Estimated. This arithmetic difference is not promised savings; it compares ready-mix-only material with a broad installed slab benchmark.
Concrete cost calculator FAQ
How much does a concrete slab cost per square foot?
This concrete slab cost calculator uses the national installed benchmark as its starting point. A standard slab averages $6–$12 per square foot installed nationallyVerified. That published HomeGuide range is dated February 3, 2026. The page uses it as a benchmark, then labels any thickness- or metro-adjusted result as Estimated rather than presenting it as a contractor bid.
How many cubic yards does a 20×20 slab need?
A 20×20 ft slab at 4 inches thick needs about 5.43 cubic yards with 10% addedEstimated. Without that allowance, the geometric volume is about 4.94 cubic yardsEstimated. Both figures come from the displayed dimensions, not from a price database.
How many 80 lb concrete bags equal one cubic yard?
One cubic yard is approximately 45 bags of 80 lb concrete mixEstimated. The calculation divides 27 ft³ by the QUIKRETE-listed yield of 0.60 ft³ per bagVerified, from its technical data sheet revised October 2022.
Does this calculator provide ZIP-code pricing?
No—location precision stops at the metro-area level. The location choices use BLS May 2025 construction and extraction wage data for named metropolitan areas. A ZIP code would imply a level of public pricing precision that the source data cannot support.
What is included in the installed cost estimate?
The result is an installed slab benchmark, not an itemized quote. It begins with HomeGuide's $6–$12/sq ftVerified national range dated February 3, 2026. A contractor's actual scope may price concrete, labor, site conditions, reinforcement, finish, delivery, overhead, and other line items differently.
Why is the metro price marked Estimated?
The metro result combines two verified datasets through a disclosed model. The national slab range comes from HomeGuide, while labor variation comes from BLS OEWS May 2025 metro wages. The calculator assumes a 45% labor shareEstimated and a 55% material shareEstimated, so the resulting dollar range is a modeled estimate.
Got a quote? Send it over—we’ll help you check whether it looks reasonable.
Enter the total from your quote and compare it with the current calculator range. The comparison runs locally in your browser.