A 30×40 concrete slab (1,200 sq ft) typically costs between $7,200 and $14,400 installed, averaging about $9,600 to $10,800 ($8 to $12 per square foot) for a standard 4-inch to 6-inch pour with labor, materials, grading, and a basic broom finish. A 30×40 dimension is the most popular size for pole barns, 3-car detached garages, workshops, and metal building foundations.
Because a 30×40 slab requires 15 to 23 cubic yards of concrete before waste, it is normally placed from multiple ready-mix trucks. Reinforcement and joint design depend on the building, loads, soil, and local requirements. Use the calculator below to compare thickness, finish, reinforcement, and state cost adjustments, then have the project specification checked locally.
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Range breakdown
| Component | Low | Average | High |
|---|---|---|---|
| Base installation | - | - | - |
| Thickness adjustment | - | - | - |
| Finish adjustment | - | - | - |
| Calculated subtotal | - | - | - |
30×40 Concrete Slab Cost Breakdown (1,200 Sq Ft)
Total cost depends on whether the slab is intended for light residential parking, a pole barn dirt-floor conversion, or heavy vehicle and tractor storage.
| Slab Specification | Thickness | Concrete Volume | Typical Cost Range | Average Cost |
|---|---|---|---|---|
| Standard Residential / Shed | 4 inches | 15.0 cu yd | $7,200 – $10,800 | $9,000 ($7.50/sq ft) |
| Standard Garage / Workshop | 5 inches | 18.5 cu yd | $8,800 – $13,200 | $10,800 ($9.00/sq ft) |
| Heavy Duty / RV & Pole Barn | 6 inches | 22.2 cu yd | $10,800 – $16,800 | $13,500 ($11.25/sq ft) |
| Commercial / Machine Shop | 6″ + Thickened Edge | 25.0 cu yd | $13,500 – $19,500 | $16,200 ($13.50/sq ft) |
What Is Included in a Turnkey 30×40 Slab Pour
- Subgrade Excavation & Grading: Clearing topsoil and grading 1,200 sq ft flat ($1,200 – $2,500).
- Compacted Gravel Base (4″ ABC): 15 to 20 tons of 3/4″ minus crushed stone compacted with a plate compactor ($600 – $1,200).
- Formwork & Staking: 140 linear feet of 2×4 or 2×6 perimeter lumber with kickers ($400 – $800).
- Vapor Barrier (10–15 mil): Common beneath enclosed, conditioned, or moisture-sensitive spaces; confirm the required material and placement with the building designer and local code ($200 – $400 planning allowance).
- Steel Rebar Grid (#4 on 18″ centers): Elevated on 2″ concrete dobie chairs ($800 – $1,400).
- Delivered Ready-Mix (4,000 PSI): 2 to 3 full concrete truckloads ($2,400 – $3,600 material).
- Labor & Finishing: 4-person crew for screeding, bull floating, hand edging, and broom finish ($3,500 – $5,500).
- Control Joints: Sawcutting 8–10 ft grid within 12 hours of pouring ($250 – $450).
30×40 Building Coordination Checklist
A 30×40 slab often becomes part of a complete building system. Before requesting a final quote, give bidders the same plan showing column reactions, anchor bolts, door thresholds, utility sleeves, drains, vehicle-lift locations, thickened edges, insulation, and finished-floor elevation. Pricing the slab before the building loads and penetrations are known can lead to costly changes after forming or reinforcement begins.
Schedule truck arrival, washout, pump or chute access, finishing equipment, curing, and sawcutting as one placement plan. Use the rebar calculator for a preliminary grid takeoff and the pump guide to compare access options.
Frequently Asked Questions About 30×40 Slabs
How many yards of concrete are in a 30×40 slab?
A 30×40 slab with a standard 4-inch thickness requires 14.8 cubic yards (16.3 cu yd with 10% waste buffer). A 5-inch slab requires 18.5 cu yd, and a 6-inch slab requires 22.2 cu yd (roughly 2 to 3 full ready-mix truckloads).
Should a 30×40 slab be 4 inches or 6 inches thick?
Four inches may be suitable for some light-duty uses, while vehicle lifts, tractors, columns, walls, or concentrated loads can require thicker or locally reinforced areas. There is no safe universal thickness: confirm loads, soil, base, concrete strength, reinforcement, and local requirements with the building supplier or a qualified designer.
Do I need a building permit for a 30×40 slab?
Many jurisdictions require zoning and building approval for a slab this size, especially when it supports an enclosed structure. Rules, plan requirements, inspections, and fees vary widely. Ask the local building department before excavation and include actual permit costs separately from the calculator result.
Related Concrete Tools
- Concrete Slab Cost Calculator (Custom Sizes)
- Rebar & Steel Takeoff Calculator
- Concrete Driveway Cost Calculator
- Ready-Mix Concrete Price Per Yard
Sources and Update Policy
Estimates are derived from monthly verified public contractor pricing and regional labor benchmarks. Review our estimation methodology.
- ConcreteNetwork — Commercial & Residential Slab Pricing
- HomeAdvisor — Garage & Outbuilding Foundation Averages
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