How much does a 40x80 concrete slab cost?
A 40x80 concrete slab cost depends on thickness, reinforcement, subbase and finish, so the total is built from line items: cubic yards of ready-mix, rebar tonnage, formwork perimeter, vapor barrier area and labor hours. We show each quantity, unit and rule so you can verify the number before you bid.
What a 40x80 Concrete Slab Cost Estimate Actually Contains
A 40 ft x 80 ft footprint is 3,200 sq ft, and that number anchors every line that follows. A 40x80 concrete slab cost estimate is not a single rate; it is a stack of line items: ready-mix concrete measured in cubic yards, reinforcement in linear feet or pounds, gravel subbase in tons or cubic yards, formwork in linear feet of edge, labor in crew hours, and finishing in square feet of troweled or broom-finished area. Each line carries a unit, a measurement rule, and a source, so you can audit the math instead of trusting a lump sum.
The calculator below does not price concrete. It is a square-foot budget tool: you enter building area, your own base hard cost per square foot, soft-cost percentage, contingency percentage, and escalation percentage, and it returns hard cost, soft costs, contingency, escalation, budget total, and all-in cost per square foot. Use it after the line-item takeoff to see how adders move the number. For the line-item side, our concrete estimating services produce a 40x80 concrete slab estimate in Excel and PDF with marked-up drawings.
Square-foot budget calculator
- Hard cost
- $444,000
- Soft costs
- $53,280
- Contingency
- $49,728
- Escalation
- $21,880
- Budget total
- $568,888
- All-in per sq ft
- $237
Enter your own base rate from a recent bid, cost book or estimator. The default values are placeholders for the math, not market prices.
Scope: what the slab price includes and excludes
Included in a typical slab-on-grade scope: excavation and grading to subgrade, a compacted gravel subbase, a vapor retarder, formwork, reinforcement, ready-mix concrete, placement, consolidation, finishing, and saw-cut control joints. Excluded unless stated: engineered fill, dewatering, termite treatment, anchor bolts and embeds, dowels at openings, pump charges, winter heating or cooling of concrete, and any permit or testing fees. The scope statement should name each exclusion, because a 40x80 shop slab cost can swing on whether the base is 4 in or 8 in of compacted stone.
Why 3,200 sq ft is the anchor number
At 3,200 sq ft, every square-foot rate you see for concrete slab cost per square foot can be checked against quantities. A 6 in slab over 3,200 sq ft is 1,600 cu ft, or 59.26 cu yd before waste. Change the thickness to 5 in and the volume drops to 49.38 cu yd; the area did not change, but the concrete line did. Keeping 3,200 sq ft fixed lets you compare thickness, reinforcement, and finish options on the same footprint. For a broader benchmark, see our concrete slab cost per square foot guide.
How Many Cubic Yards of Concrete Does a 40x80 Slab Need?
Concrete is ordered in cubic yards, and the conversion is fixed: area in square feet times thickness in feet gives cubic feet; divide by 27 for cubic yards. For 3,200 sq ft at 4 in thick, the math is 3,200 x 0.3333 = 1,066.67 cu ft, or 39.51 cu yd. At 5 in, 3,200 x 0.4167 = 1,333.33 cu ft, or 49.38 cu yd. At 6 in, 3,200 x 0.5 = 1,600 cu ft, or 59.26 cu yd. Those are net quantities; the order quantity adds waste.
The calculator below takes length, width, thickness, and waste percentage and returns area, cubic feet, net cubic yards, and order quantity. Use it to check the ready-mix ticket before you call the plant. For a worked walkthrough of the same arithmetic on a similar footprint, see our sample slab quantity survey, and for crews priced by the hour on placement and finishing, our trade estimating services show how those labor lines are built.
Slab quantity takeoff
- Area
- 2,400 sq ft
- Volume
- 800 cu ft
- Net concrete
- 29.63 cu yd
- Order quantity
- 31.11 cu yd
Formula: length × width × (thickness ÷ 12) ÷ 27 = cubic yards. Thickened edges, footings and pump waste are taken off separately.
Thickness drives volume: 4 in vs 5 in vs 6 in
A 40x80 concrete slab thickness and rebar decision is a design decision, not a pricing preference. A 4 in slab is common for residential patios and shed floors; 5 in is a middle ground for light-duty shop floors; 6 in is typical for barndominium slabs, vehicle lifts, and heavier equipment. Each 1 in of thickness over 3,200 sq ft adds 9.88 cu yd of concrete. That is why the 3200 sq ft concrete slab cost is not a single number: the same area at 4 in and 6 in differs by 19.75 cu yd of ready-mix before waste.
Waste and over-order allowance
A 5–10% waste and grade allowance covers spillage, uneven subgrade, form deflection, and the last-yard shortfall that stops a pour. On 59.26 cu yd net, 5% is 2.96 cu yd and 10% is 5.93 cu yd, so the order quantity ranges from about 62.22 to 65.19 cu yd. Ordering short and adding a second truck mid-pour risks a cold joint and extra saw cut layout; ordering long leaves you with a returned-load charge. The waste factor belongs on its own line, not buried in the unit rate.
Worked Example: 40x80 Concrete Slab Cost at Stated Assumptions
This worked example is illustrative. Every rate below is a stated input, not a market average; replace them with your supplier quotes and local labor rates. The assumptions: 3,200 sq ft slab on grade, 6 in thick, 4 in compacted gravel subbase, 15 mil vapor barrier, #4 rebar at 18 in on center each way, 6 in turndown edge, saw-cut control joints at 15 ft spacing, and a broom finish. Quantities are net; waste is shown separately.
The calculator below takes a base estimate and an AACE estimate class from 5 to 1 and returns low and high contingency plus a budget range. Use it to test how the class of your estimate changes the contingency line, not to price the concrete itself. For help building the line-item side, our professional concrete estimating services deliver a 40x80 concrete slab estimate with the arithmetic exposed.
| Line item | Quantity | Unit | Illustrative unit rate | Extended cost |
|---|---|---|---|---|
| Ready-mix concrete (10% waste included) | 65.19 | cu yd | $165.00 | $10,756.35 |
| #4 rebar at 18 in o.c. each way | 4,695 | lin ft | $0.85 | $3,990.75 |
| Gravel subbase, 4 in compacted | 55.31 | ton | $28.00 | $1,548.68 |
| Vapor barrier, 15 mil | 3,520 | sq ft | $0.15 | $528.00 |
| Formwork at perimeter | 240 | lin ft | $4.50 | $1,080.00 |
| Saw-cut control joints | 360 | lin ft | $2.00 | $720.00 |
| Labor, blended crew rate | 120 | hour | $38.00 | $4,560.00 |
| Direct cost subtotal | $23,183.78 |
Contingency range by estimate class
- Low contingency
- $150,000 (10%)
- High contingency
- $300,000 (20%)
- Budget range
- $1,650,000 – $1,800,000
Typical planning ranges that follow the AACE estimate-class idea: less design, more contingency. Set the final figure from a risk review of your own project.
Assumptions and unit rates used
Concrete: 59.26 cu yd net, 10% waste = 65.19 cu yd ordered, at an illustrative $165 per cu yd. Rebar: #4 at 18 in o.c. each way over 3,200 sq ft gives 2,134 lin ft each direction, 4,268 lin ft total, plus 10% laps and waste = 4,695 lin ft at an illustrative $0.85 per lin ft. Gravel subbase: 3,200 sq ft x 0.3333 ft = 1,066.67 cu ft; at 1.4 tons per cu yd, that is 55.31 tons at an illustrative $28 per ton. Vapor barrier: 3,200 sq ft plus 10% laps = 3,520 sq ft at $0.15 per sq ft. Formwork: perimeter 240 lin ft plus interior saw-cut layout; 240 lin ft at $4.50 per lin ft. Saw-cut control joints at 15 ft spacing: 5 cuts across the 80 ft length × 40 ft plus 2 cuts across the 40 ft width × 80 ft = 360 lin ft at $2.00 per lin ft. Labor: 120 crew hours at an illustrative blended $38 per hour.
Quantities x unit rates, line by line
Concrete: 65.19 cu yd x $165 = $10,756.35. Rebar: 4,695 lin ft x $0.85 = $3,990.75. Gravel: 55.31 tons x $28 = $1,548.68. Vapor barrier: 3,520 sq ft x $0.15 = $528.00. Formwork: 240 lin ft x $4.50 = $1,080.00. Saw-cut joints: 360 lin ft x $2.00 = $720.00. Labor: 120 hours x $38 = $4,560.00. The direct cost subtotal is $23,183.78, or $7.24 per square foot. Check each multiplication against its unit: cubic yards, linear feet, tons, and square feet are not interchangeable, and a rate quoted in the wrong unit is the most common line-item error. A sample takeoff walkthrough shows the same unit checks applied to a full sheet.
Totals before and after soft costs and contingency
Add 8% contingency to the direct subtotal: $23,183.78 x 0.08 = $1,854.70, bringing the hard-cost budget to $25,038.48. Add 12% soft costs for engineering, permits, and testing: $25,038.48 x 0.12 = $3,004.62, for a total budget of $28,043.10, or $8.76 per square foot. If you are pricing a 40x80 barndominium slab cost, the same quantities apply but the finish schedule and anchor-bolt layout may add lines. For a full commercial construction cost estimate format, see our commercial construction estimate page.
What Drives the Price of a 40x80 Concrete Slab
A 40x80 slab is 3,200 square feet of flatwork, and the drivers that move its price are the same ones an estimator reads off the drawings before pricing anything. Each driver lands on a named line in the estimate, which is why two bids for the same footprint can differ by thousands of dollars without either contractor being wrong. The calculator below converts the wage table's base rates into a loaded crew rate, so you can see how burden and overtime change the labor half of every line.
Loaded labor rate calculator
- Loaded rate
- $31/hr
- Blended with overtime
- $32/hr
- Labor hours
- 320
- Crew labor cost
- $10,279
Burden covers payroll taxes, workers’ compensation, insurance and benefits; it varies by state, trade and company. Overtime is priced at time and a half.
Slab thickness, reinforcement, and subgrade
Thickness multiplies directly into volume: 3,200 square feet at 4 inches is about 39.5 cubic yards, at 6 inches about 59.3 cubic yards, before any waste factor. Reinforcement follows the same logic. A wire mesh schedule prices by roll or sheet area, while a two-direction rebar mat prices by linear feet at a stated spacing, and the rebar worker hours rise with bar count rather than slab area. Subgrade is the line owners underestimate: strip topsoil, proof-roll, and compact a gravel base, and the base course depth on the grading plan sets both tons hauled in and compaction passes. In the worked example above, the thickness and reinforcement lines carry the largest share of material cost, and the base prep line carries the largest share of equipment and labor hours.
Access, site conditions, and haul distance
A ready-mix truck needs a path it can actually drive, and the pump or chute reach sets how the pour is staged. Tight access off an alley, a steep grade, or a backyard pour past a fence line adds pump setup time and sometimes a conveyor, and those costs land in a separate access line rather than hiding in the concrete rate. Haul distance from the plant matters because mix design has a working time; a long run can force retarder or a smaller load size, and short loads price differently per cubic yard than full ones. Wet, soft, or rocky subgrade raises excavation and backfill quantities, and any unsuitable material has to be hauled off, which is a disposal line the bid should show.
Finish, joints, and curing method
Finish level is a crew-hours decision. A broom finish on a shop floor takes far fewer cement mason hours than a burnished power-trowel finish, and a stamped or saw-cut pattern adds layout and tooling time per square foot. Control joints are priced by linear foot of saw cut, so joint spacing on the plan converts into a quantity, and the curing method (cure-and-seal compound, wet cure, or blankets) is its own line with its own material and labor. The concrete slab cost per square foot you compare across bids only means something when each bid states the same finish, joint spacing, and curing method; otherwise you are comparing different scopes.
Material Price Movement You Can Verify Yourself
The cost of concrete for a 40x80 slab moves with two published series you can pull yourself: ready-mix concrete and steel mill products, the parent series for reinforcing bar. The chart below rebases those BLS Producer Price Index series to 100 so you can see relative movement instead of absolute index values. An estimator who can read the series can defend a material line in a bid review without relying on a supplier's verbal quote, and knowing how much is a yard of concrete in the current market keeps the ready-mix line anchored to a published rate rather than a phone call.
Material price movement, Oct 2023 to Sep 2026
Reading PPI series for ready-mix and rebar
Go to the BLS Producer Price Index database and pull the series for ready-mix concrete and for steel mill products, using the same monthly or annual period for both. Record the index value at the base date and at the current date, then divide the change by the base value to get a percentage. That percentage is what you apply to the material portion of your line, not to the whole line, because labor and equipment do not move with the commodity. A wire mesh or rebar mat line should be split so the steel portion is visible and adjustable, and a ready-mix line should show the quoted cubic yard rate separately from the placing labor. The rebar worker hours stay on the labor side and are adjusted from wage data, not from the steel index.
Turning an index change into a rate change
Suppose a ready-mix line in your estimate is $180 per cubic yard and the ready-mix index rose a stated percentage over the period you are pricing to. Multiply the rate by the percentage, add the result to the original rate, and carry the new rate into the extended quantity. Do the same for the steel portion of the reinforcement line, keeping the bar quantity and the placing hours unchanged. Show the base index date, the current index date, and the arithmetic on the estimate sheet so a reviewer can retrace it. When the pour is months out, note which index date the bid is pinned to and whether an escalation clause applies; that single note prevents most material disputes after award. If you want the material quantities behind those percentages checked first, a worked takeoff walkthrough shows how the cubic yards and bar lengths are derived.
How to Check a 40x80 Concrete Slab Bid Line by Line
A 40x80 shop slab cost is easy to quote as one number and hard to audit, so ask for the breakdown before you compare totals. Start with thickness and reinforcement: the bid should state the slab thickness in inches, the reinforcement type and spacing, and whether a vapor barrier is included under the slab. Next, verify the waste allowance on the concrete line; a stated percentage is normal, an unexplained lump is not. Confirm base prep is a separate line covering excavation, compaction, and the gravel subbase depth, and confirm haul-off of unsuitable material is priced or explicitly excluded. Finally, check that control joints, saw cut linear footage, and the curing method appear as line items rather than as a note. A second set of eyes on the same drawings is worth the cost once; professional concrete estimating services can cross-check quantities against the bid before you sign.
Red flags in lump-sum slab bids
A single lump sum with no thickness, no rebar mat description, and no vapor barrier note cannot be compared to another bid. Watch for a concrete quantity that does not reconcile with the footprint times thickness, a missing compaction or base course line, and reinforcement described only as "mesh" without a gauge or spacing. A bid that omits curing and joints is not necessarily cheap; those costs often reappear as a change order after pouring starts. Ask for the marked-up drawing pages that show where each quantity came from.
Questions to ask before signing
Ask which code edition and which ACI 318 provisions govern the slab design, and confirm the local building department's adopted edition, since that governs cover and joint details. Ask who provides and installs anchor bolts, dowels, and turndown edges at the perimeter, and whether formwork for those edges is in the base bid. Ask how the contractor handles a failed compaction test or unsuitable subgrade found after excavation. Ask for the curing method in writing and the joint layout on a plan sheet. If the answers are verbal only, put them in the bid documents before award. When you want the arithmetic checked, send your plans and we will return a line-item estimate with the measurement rules shown.
Frequently Miscalculated Items on a 40x80 Slab
Most of the gap between two bids on the same 3,200 sq ft slab sits in scope lines that are easy to skip and expensive to add after the forms are set. A 40x80 concrete slab cost built from a real takeoff shows each of those lines with its own unit, quantity and rule, which is what makes the totals comparable. Before you compare a lump sum from anyone, ask for the line-by-line quantity takeoff behind it.
To start, request a free quote and attach your drawings.
| Line item | Correct unit | Typical miss |
|---|---|---|
| Vapor retarder, 15-mil, lapped | sq ft of membrane | Omitted entirely |
| Gravel base course, 6 in. compacted | cu yd loose or ton | Priced as 4 in. or skipped |
| Compaction passes | hr or sq ft | No equipment line |
| Concrete, 6 in. slab | cu yd incl. waste | Neat volume ordered |
| Rebar mat, #4 at 18 in. o.c. | linear ft incl. laps | Chairs and dowels left out |
| Formwork at turndown edge | linear ft of edge | Priced inside slab sq ft |
Forgetting vapor barrier and base compaction
Two lines go under the slab and neither shows up in a photograph once the concrete is placed: the vapor retarder and the compacted base course. A 40x80 footprint is 3,200 sq ft, so a 15-mil vapor retarder with 12 in. laps and a 6 in. gravel subbase are both large quantities — roughly 3,200 sq ft of membrane and about 593 cu yd of compacted aggregate at 6 in. (3,200 × 0.5 ÷ 27). Estimators who price the slab surface only and stop there leave both out. Compaction is measured in passes with a plate or roller and verified against the grading plan; a bid that lists no compaction equipment or proof-rolling line has not priced it.
Under-ordering concrete and paying short-load fees
A 40x80 slab at 6 in. is 3,200 × 0.5 ÷ 27 = 59.26 cu yd neat, and at 5 in. it is 49.38 cu yd. Add a typical 5% waste factor and the 6 in. order becomes 62.2 cu yd; round to full truck loads and the order is 63 cu yd. Ordering 59 cu yd against a 62.2 cu yd need leaves the crew short mid-pour, and a short load or a second dispatch usually costs more than the surplus concrete. The same error appears on the rebar mat: #4 at 18 in. on center each way over 3,200 sq ft is about 4,300 linear ft before laps, and laps, chairs and dowels at construction joints are routinely omitted. Confirm slab thickness and reinforcement with the structural drawings and ACI 318 provisions adopted by your building department before the order is placed.
Frequently Asked Questions
How much does a 40x80 concrete slab cost?
A 40x80 concrete slab cost is built from quantities, not a square-foot guess: 3,200 sq ft times thickness gives cubic yards, then ready-mix, rebar, forms, base, labor and finishing are priced as separate lines. The fee for an estimate is quoted per project after we review the plans, because thickness, reinforcement and site access change the arithmetic.
How many yards of concrete do I need for a 40x80 slab?
At 4 inches, 3,200 sq ft needs about 39.5 cubic yards; at 6 inches, about 59.3 cubic yards. The rule is square feet times thickness in feet divided by 27. Add a waste factor for spillage and uneven subgrade, and order in full yards, since ready-mix trucks do not split a yard at the chute.
Is a 4-inch or 6-inch slab better for a 40x80 shop?
A 6-inch slab suits a 40x80 shop carrying vehicles, lifts or heavy racks; 4 inches is common for light storage and residential flatwork. Thickness drives both concrete volume and reinforcement cover, so confirm the design with the engineer of record and the local building department's adopted code edition before pricing.
How much rebar does a 40x80 slab need?
For a 40x80 mat at 18 inches on center each way, figure roughly 4,270 linear feet of bar (about 2,130 feet each way) plus lap and waste, then convert to weight by bar size. Spacing, bar diameter and the number of mats come from the structural drawings. Wire mesh is a separate line item and is not a substitute for a designed rebar mat.
Does a 40x80 concrete slab cost estimate include site prep?
Only if the line items say so. Grading, compaction, gravel subbase and vapor barrier are separate scopes from concrete supply and finishing, and a bid that omits them is not comparable. Send the grading plan and finish schedule with the drawings so those quantities are measured rather than carried as an allowance.
How do I check a concrete contractor's slab bid?
Check four things: the thickness and reinforcement stated, the cubic yards ordered against your own calculation, whether base, vapor barrier and saw-cut control joints appear as lines, and the unit each price uses. A lump sum hides all four. Our quantity takeoff example shows how the same slab is measured line by line.
Can you use my estimate template?
Send the template with the plans and we confirm whether the estimate can be delivered in it. The workbook we return is organized by CSI MasterFormat division with quantities, units and measurement rules visible, so it can be mapped into your format where the line structure allows.
Do you sign NDAs before reviewing drawings?
Clients can request one before sending drawings, and the terms are agreed before plan review begins. Send the request with the plan set so the scope and confidentiality terms are settled before any quantity work starts.