A 24-by-35-foot concrete slab covers 840 square feet and typically costs $5,040-$12,600 installed, with an average near $8,400 for a standard residential pour. Thickness, reinforcement, site preparation, regional labor rates, and access to the pour can shift the estimate substantially.
| Item | Low | Average | High | Notes |
|---|---|---|---|---|
| Installed 840-sq-ft slab | $5,040 | $8,400 | $12,600 | $6-$15 per sq ft; ordinary access and residential concrete |
| Concrete and delivery | $2,100 | $3,150 | $4,200 | About 14-21 cubic yards, depending on thickness and waste |
| Site preparation | $500 | $1,250 | $3,000 | Minor grading through substantial excavation and base work |
| Reinforcement and finish | $400 | $1,050 | $2,500 | Mesh or rebar, joints, and finish level affect price |
What an 840-square-foot slab usually costs
For a straightforward slab with a compacted gravel base, basic reinforcement, and a standard broom finish, budget roughly $6-$10 per square foot, or $5,040-$8,400 total. A thicker slab, difficult grading, premium finish, or higher-cost market can bring the installed rate to $12-$15 per square foot.
A practical planning figure is about $8,400 for a standard 4-inch slab with ordinary site access. This assumes a rectangular pour, no demolition, no major drainage correction, and no special structural engineering. A garage or building foundation may require thicker edges, footings, or code-specific reinforcement not included in a basic patio-style estimate.
Assumptions: 840 square feet, residential concrete, typical Midwest labor, standard broom finish, and a prepared or moderately level site.
How concrete, crew labor, and base work shape the quote
Concrete volume helps explain material costs. At 4 inches thick, 840 square feet requires about 10.4 cubic yards before waste; ordering roughly 11-12 yards is common. At 6 inches, the slab needs about 15.6 cubic yards before waste, often requiring a 16-17-yard order. Ready-mix pricing varies by market, mix specification, delivery distance, and short-load fees.
| Quote component | Low | Average | High | Typical scope |
|---|---|---|---|---|
| Concrete and delivery | $2,100 | $3,150 | $4,200 | Ready-mix, delivery, and ordinary ordering allowance |
| Labor | $1,500 | $2,600 | $4,000 | Forming, placing, finishing, and jointing |
| Base and site preparation | $500 | $1,250 | $3,000 | Gravel, compaction, grading, and limited excavation |
| Reinforcement and forms | $400 | $850 | $1,600 | Mesh or rebar, lumber forms, and supports |
| Equipment and disposal | $200 | $550 | $1,400 | Small equipment, haul-off, or pump if required |
Labor commonly accounts for $1.75-$4.75 per square foot, while material and preparation make up much of the remaining quote. Contractors may combine tasks into a single installed rate, so written estimates should identify what the total includes.
Thickness, reinforcement, and grading that change the price
Slab thickness is a major price driver because it changes both concrete volume and structural capacity. Moving from 4 inches to 6 inches adds about 5.2 cubic yards before waste for this footprint; that can add several hundred dollars to material and handling. Vehicle loads, heavy equipment, and building use may require an engineered design rather than a standard residential specification.
Reinforcement can range from welded wire mesh to rebar grids. Depending on material and spacing, expect roughly $0.50-$2.00 per square foot for reinforcement supply and placement. A sloped or uneven site may need extra excavation, fill, compaction, or retaining work; a difference of more than 6-12 inches across the pad can make grading and drainage noticeably more expensive.
Confirm the specified thickness, edge details, reinforcement, and base depth before comparing per-square-foot bids. A low quote may omit compacted stone, thickened edges, control joints, or disposal, making it unlike a more complete estimate.
How regional labor rates affect an 840-square-foot pour
Local labor, concrete supply, and delivery access can move a slab estimate well away from the national planning range. In lower-cost rural and Midwestern markets, a basic installation may fall near the lower end; dense metro areas and high-cost coastal markets can run 15%-35% higher. Remote sites may also face travel charges or limited supplier availability.
Compare local bids on the same written scope rather than relying on a national average alone. Ask whether the quote includes concrete delivery, gravel depth, reinforcement, finishing, curing provisions, and cleanup. A pump may add about $500-$1,200 when the truck cannot discharge close to the forms; difficult access or long placement distances can raise the charge further.
What three realistic slab quotes can include
These examples show how scope changes the total for the same 840-square-foot footprint. Rates vary by city, season, and contractor, and totals are illustrative rather than guaranteed local prices.
| Scenario | Specifications | Estimated total |
|---|---|---|
| Basic patio pad | 4 inches, modest gravel base, mesh, broom finish, easy access | $5,500-$7,000 |
| Typical garage slab | 4 inches with reinforced edges, rebar or mesh, compacted base, control joints | $7,500-$10,000 |
| Heavy-duty or difficult site | 6 inches, heavier reinforcement, grading, pump or restricted access | $11,000-$15,500 |
The garage and difficult-site examples cost more because they add structural details, site work, or placement equipment. A garage foundation may also need footings, vapor barrier, insulation, or inspections, which should appear as separate quote line items.
How long forming and finishing take on a 24-by-35 slab
A small crew may spend 1-3 days on excavation, base preparation, and forms, then place and finish the concrete in one pour day. Curing continues after the crew leaves; light foot traffic is often restricted for at least 24-48 hours, while vehicle use may need to wait about 7 days or longer based on the mix and weather.
Labor estimates are easier to compare when the contractor lists preparation days and pour-day crew work separately. A rough labor calculation uses 30-55 crew hours at about $50-$90 per worker-hour, but contractors often quote the job as a project total rather than billing hourly.
Which add-ons can raise a concrete slab estimate
Old slab removal commonly adds about $2-$6 per square foot, including breaking and hauling, depending on thickness and disposal fees. Excavation and soil removal may add $1-$5 per square foot where the grade or soil is poor. A concrete pump often costs $500-$1,200, and a short-load or difficult delivery can add several hundred dollars.
Request separate prices for demolition, pumping, extra gravel, drainage, and edge thickening. Permits are location- and project-specific; a simple patio may not require one, while a garage foundation or building slab may need permits, inspections, and plan review fees. Verify requirements with the local building department before work begins.
Ways to lower the slab price without weakening the design
Keep the footprint rectangular, clear brush and loose debris before the crew arrives, and confirm truck access early. If the slab is for light-duty use, ask a qualified contractor whether a standard 4-inch design meets local requirements instead of paying for unneeded thickness or structural upgrades.
Compare at least three itemized bids using the same dimensions, thickness, base, reinforcement, and finish. Avoid cutting necessary compaction, drainage, or reinforcement to chase a low price; defects can be costly to repair. Scheduling outside the busiest local construction period may help with contractor availability, although weather and supplier pricing still affect the final estimate.