A 20×40 concrete slab (800 sq ft) typically costs between $4,800 and $9,600 installed, with national averages landing between $6,400 and $7,600 ($8 to $10 per square foot) for a standard 4-inch to 6-inch pour including site grading, gravel base, #4 rebar reinforcement, and a non-slip broom finish.
A 20×40 slab is one of the most versatile dimensions in residential construction—commonly built for RV and camper parking pads, 2-car tandem garages, detached workshops, large backyard patios, and half-court basketball pads. Because it requires 10 to 16 cubic yards of concrete, it is poured with 1 to 2 full ready-mix concrete trucks. Use the interactive calculator below to price your exact thickness, rebar grid, and state labor rate.
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Range breakdown
| Component | Low | Average | High |
|---|---|---|---|
| Base installation | - | - | - |
| Thickness adjustment | - | - | - |
| Finish adjustment | - | - | - |
| Calculated subtotal | - | - | - |
20×40 Concrete Slab Cost Breakdown (800 Sq Ft)
| Application / Use Case | Thickness | Concrete Volume | Turnkey Price Range | Average Cost |
|---|---|---|---|---|
| Outdoor Patio / BBQ Living Area | 4 inches | 10.0 cu yd | $4,800 – $7,200 | $6,000 ($7.50/sq ft) |
| Standard 2-Car Garage / Workshop | 4 inches (Rebar) | 10.0 cu yd | $5,600 – $8,000 | $6,800 ($8.50/sq ft) |
| Heavy Duty RV & Boat Parking Pad | 6 inches (Heavy) | 15.0 cu yd | $7,200 – $11,200 | $9,200 ($11.50/sq ft) |
| Stamped / Decorative Pool Surround | 4 inches (Stamped) | 10.0 cu yd | $9,600 – $14,400 | $11,800 ($14.75/sq ft) |
20×40 Slab Material Takeoff & Cost Breakdown
- Ready-Mix Concrete: 10 to 15 cubic yards delivered (1 to 2 truckloads) at $145–$185/yd ($1,500 – $2,700).
- Crushed Gravel Subbase (4″ ABC stone): 10 to 14 tons compacted ($400 – $800).
- Rebar Grid (#4 1/2″ bars @ 18″ spacing): 60 standard 20-ft rebar sticks + 45 dobie chairs ($600 – $1,000).
- Perimeter Forming Lumber (120 linear feet): 2×4 or 2×6 forms with wooden kickers ($250 – $450).
- Contractor Labor & Equipment: Excavation, grading, screeding, bull floating, and control joint sawcutting ($3,000 – $5,200).
20×40 Planning Decisions That Change the Quote
- RV or boat pad: Give the contractor axle loads, parking position, turning path, and whether stabilizer jacks will create concentrated loads.
- Garage or workshop: Mark door openings, floor drains, anchor-bolt lines, utility sleeves, lift locations, and any thickened areas before reinforcement is ordered.
- Outdoor recreation: Confirm slope, drainage destination, surface texture, and joint layout so water and joints do not interfere with play.
- Truck access: Compare direct chute access with a line-pump allowance using the pump truck cost guide.
Frequently Asked Questions About 20×40 Slabs
How many cubic yards of concrete are in a 20×40 slab?
A 20×40 slab at 4″ thickness requires 9.88 cubic yards (order 11 cu yd with 10% waste buffer). A 5″ slab requires 12.35 cu yd, and a 6″ slab requires 14.81 cu yd.
How thick should a 20×40 RV parking pad be?
Six inches with reinforcement is a common planning assumption for heavy RV use, but it is not a universal specification. Vehicle weight, axle and jack loads, soil, base compaction, drainage, frost conditions, concrete strength, and local code can change the design. Ask a qualified local professional to specify the slab for the actual vehicle and site.
How many control joints does a 20×40 slab need?
Control joints should be spaced at intervals no greater than 24 to 30 times slab thickness (roughly 8 to 10 feet apart). A 20×40 slab requires 1 center joint lengthwise (at 10 ft) and 3 cross joints (at 10 ft, 20 ft, and 30 ft) to create eight 10×10 panels.
Related Tools
- Concrete Slab Cost Calculator (Custom Sizes)
- Rebar Quantity Takeoff Tool
- Concrete Driveway Cost Calculator
- Delivered Concrete Price Per Yard
Sources and Update Policy
Installed-price assumptions use ConcreteNetwork’s concrete pricing reference as a public baseline and are checked monthly. Read our estimation methodology.
Estimate transparency
How this estimate was prepared
- Prepared by
- GoHomeCost Cost Data Team
- Last reviewed
- August 24, 2026
- Update cycle
- Public price inputs checked monthly
Calculation method: Project quantity is multiplied by editable low, typical, and high unit rates. Selected location adjustments, waste, fixed charges, and minimum-job rules are then applied and shown in the result.
Public references used on this page:
This is a planning estimate, not a quote or structural specification. Check product yields, local code, site conditions, and written contractor bids before purchasing materials or building.
Read the full methodology Report a price or calculation issue