How Much Does a Concrete Slab Cost?

The curve, from a contractor's own price list

Day's Concrete Floors publishes two complete by-size tables and states the mechanism in his own words: "Whether the concrete slab is 10' x 10' or 16' x 12', the time (labor) is pretty much the same." That is the whole argument. The crew, the forms, the trowel and the truck trip do not shrink with the slab.

Read the last column. His pricing model is a marginal rate times the area, with a floor underneath it. The floor is worth $1,300 to $1,650 on a small slab and it vanishes at about 400 square feet. Fit a straight line to his four 4-inch rows and you get roughly $1,420 fixed plus $2.85 per square foot, which reproduces his 10 by 10 and his 20 by 20 to within half a percent and the two middle rows to within 2.5. That is the shape of a slab price, and it is why "what does concrete cost per square foot" has no single answer.

His two 4-inch rates differ by nearly a factor of two, $6.40 per square foot on the shed table against $12.00 on his general slab page, and that is scope rather than contradiction: the shed figure excludes excavation, the gravel base, a power trowel finish and saw-cut joints. Which brings up the thing that matters more than any number on this page, and it is in the next section.

The number you are quoted probably excludes the ground

Two of the sources in this topic state their scope. Both of them exclude the same thing, and it is large.

• Homewyse, verbatim, on both its concrete pad and cement slab pages: the estimate "excludes excavation, gravel base layer, compaction or hardscape demolition."
• Day's Concrete Floors, on three separate pages: digging, gravel, compacting and leveling is $5.00 per square foot and is not in his slab price. On the 40 by 24 job he itemizes, that was $4,800 on top of an $11,520 slab, a 42 percent uplift. On the 30 by 30, $4,500.

Everyone else is silent on whether it is in or out. HomeGuide prices the same layer at $1 to $3 per square foot plus grading at $0.40 to $2.00. Our own derivation from Wisconsin DOT's in-place tonnage puts 4 inches of compacted granular base at $0.38 per square foot of material.

So the published spread on the work under the slab is $0.38 to $5.00 per square foot, a factor of thirteen, which is wider than the entire published spread on the finished slab itself. When two quotes for the same slab arrive hundreds of dollars apart, this is the most likely reason, and no cost guide tells you to ask. Ask whether excavation, the gravel base and compaction are in the number, and get it in writing.

Cost by slab size

Four columns, because there is no single honest answer. Sizes are written the short way, so 30x40 is the same slab as a 30 x 40 or a 30 by 40, 1,200 square feet. Ready-mix at list is the concrete at 4 inches priced at our $160 per cubic yard delivered default, which is the floor nothing can go below. It is deliberately the list figure: every size above except the last four is under a typical truck minimum, so a supplier would add a short load fee on top, and the calculator does. Flat rate is what the aggregator consensus of $6 to $12 per square foot says. Fixed plus rate is the contractor model above, fitted at about $1,420 fixed plus $2.85 per square foot, which is what falls out when you solve for both using his own published $1,700 on a 10 by 10 and $2,560 on a 20 by 20. His stated labor minimum is $1,250, so the fitted fixed charge sits a little above it, which is what you would expect from a minimum that also has to carry a short load. The published range column collects what real sources print for that size.

One reconciliation, because the column and our own calculator do not agree and the difference is the point of this page. The ready-mix column prices the concrete at the $160 per yard list default. The slab cost calculator adds a short load surcharge below a 10 yard truck minimum, which works out at $30 a yard on top, so it returns $235 rather than $198 on a 10 by 10 and $938 rather than $790 on a 20 by 20. The calculator is closer to what a supplier will actually bill; the table column is the list-rate floor. Both are useful and neither is the finished price.

Two warnings on how to read that. The fixed-plus-rate column is fitted to one contractor's shed-scope prices in one state, so it excludes excavation, gravel, a power trowel finish and saw cuts, and it falls below the flat consensus above about 400 square feet for exactly that reason. Add the $5.00 per square foot of ground work and the large sizes land back inside the $6 to $12 band. The column earns its place at the small end, where it is the only one of the three that behaves like a real invoice. The last two rows, 50 by 60 and 40 by 80, are extrapolation: his largest published job is nothing like that size, and at 3,000 square feet you are buying from a commercial flatwork crew on a unit-price contract, not from a shed contractor's price list.

The ready-mix column is the useful floor. On a 10 by 10 slab the concrete at list is $198, or about $235 once a supplier adds the short load fee, and the aggregator consensus says the finished job is $600 to $1,200, implying $400 to $1,000 covers forms, base, steel, a crew for a day and the drive. One contractor's labor minimum alone is $1,250. The slab cost calculator works your own dimensions with editable prices, and concrete price per yard has the delivered prices and the fee schedule behind that first column.

Cost by square footage, if you know the area but not the dimensions

Plenty of people arrive with a number rather than a rectangle: a 400 sq ft concrete slab, a 1,000 sq ft shop floor, 1,800 sq ft of shed and parking apron that is not a neat shape at all. Every published pricing model on this page runs on area alone, so the figures are the same ones, indexed the way you already have them.

One thing area alone cannot tell you, and no published table accounts for it. A 10 by 40 slab and a 20 by 20 slab are both 400 square feet, and every rate table on the internet prices them identically. But the 10 by 40 has 100 linear feet of perimeter against the 20 by 20's 80, so it needs 25 percent more forming for the same concrete. Forming is the one cost that scales with perimeter rather than area, which is the mechanism behind the whole per-foot curve on this page, and it is why a long narrow apron quotes higher per square foot than a square pad of the same size. If your slab is long and thin, expect to land toward the top of the band rather than the middle.

The same arithmetic runs in reverse for anything smaller than these rows. The pad cost calculator is the one to use under a cubic yard, where a supplier bills a multiple of list rather than the list rate. For the small structures that drive most of these areas, a slab for a shed covers the 8x12 to 12x20 range with the thickness and base specifics, and a slab for a garage covers 20x20 up through 30x40 with the PSI and slope requirements a shed slab does not have.

Why small slabs are brutal, in three stacked mechanisms

The per-foot rate falls with size for three separate reasons that compound. All three are measurable.

One: the minimum job charge. The dominant term, and almost nobody publishes it. Day's Concrete Floors publishes it twice in dollars, $1,250 for labor under 20 by 20 and $1,500 for a 10 by 10. Two aggregators put a minimum at $500 to $900, and the same publisher gives two different figures on two of its own pages. A contractor-software vendor's worked travel and setup example comes out near $400. The contractor-side numbers are two to four times the aggregator-side numbers, and the contractor is the one sending the invoice. Craftsman's National Construction Estimator, a professional estimating manual, carries the same idea as a rule: "Add 30% to 50% on small jobs where fitting and matching of materials is required, adjacent surfaces have to be protected and the job site is occupied during construction."

Two: the concrete itself is billed at a multiple below one cubic yard. A 10 by 10 slab at 4 inches is 1.23 cubic yards, which is under most published ready-mix minimums. Across seven suppliers in five states the effective price per cubic yard runs $228 to $340 at a 10 by 10 and $173 to $221 at a 20 by 20, against list rates in the $150s and $160s. At a 4 by 4 pad it reaches 8 to 12 times list. Concrete pad cost has the supplier-by-supplier table; the short version is that it stops mattering at about five cubic yards.

Three: forming is priced by the perimeter, and perimeter does not scale with area. This one is pure geometry. Double a square slab's side and the area quadruples while the edge only doubles. Homewyse prices wood formwork at $4.45 to $5.44 per square foot of contact area, which on a 4 inch slab is about $1.48 to $1.81 per linear foot of edge.

A 4.8-fold fall from geometry alone, with no assumption about anybody's behavior. It is the cleanest demonstration of the mechanism and the smallest of the three in absolute terms, about $0.50 per square foot of swing. The minimum charge is the big one.

The people who buy the most concrete price the curve explicitly

If the quantity effect were imaginary, the biggest buyers of flatwork in the country would not write it into their paperwork. They do.

North Carolina DOT splits one pay item by quantity on its concrete contracts. On Division 8 contract 11502347, opened 23 June 2015, five contractors bid the same specification on the same day at two quantity bands:

Five out of five priced the small band higher. Excluding the outlier the ratios run 1.37 to 1.66. The pattern repeats on a different contract six years later: on Division 8 contract 11972450 in June 2021, the same item was $39.95 per linear foot on 200 feet against $26.75 on 500 feet, a ratio of 1.49. Six bidder observations across two contracts six years apart, every one pointing the same way, mean ratio about 1.50.

The same documents show mobilization bid as its own line: $2,495 each, seven of them, $17,465 on a $163,830 contract in 2021, which is 10.7 percent of the job before any concrete is placed. In 2015 five bidders put mobilization at $5,750, $5,000, $5,000, $14,784 and $22,500.

Contracted flatwork prices from those same bid tabs, converted from square yards, give a useful sanity check on residential figures: 4 inch sidewalk at a median of $5.56 per square foot on 900 square feet, 6 inch slab at $8.89 on 225 square feet, 6 inch driveway at $8.89 on 675 square feet. Those carry traffic control and often prevailing wage, so they are a ceiling rather than a comparison, but they are real prices somebody paid.

Who publishes a flat rate, and what it costs them

We checked thirteen published by-size tables. Eight of them are the area multiplied by a constant.

The two that show a real curve are the two with something behind them: a working contractor publishing his own prices, and a site that states it calibrated its labor to the Bureau of Labor Statistics wage series for cement masons and concrete finishers. Everything else is one number times an area.

Four things we found while checking, all verifiable on the pages themselves:

• slabcalc.co names the mechanism and then denies it. Its prose says small jobs cost more "due to contractor minimums and higher edge-to-area ratios," and its table then prints exactly $6.00 and $12.00 across nine rows from 100 to 1,600 square feet. It also publishes two different minimums, $500 to $800 and $600 to $900, on two of its own pages.
• HomeGuide's $12 ceiling is, by its own arithmetic, an 8 inch slab. Its by-thickness table on the same page puts 4 inches at $6 to $8 and 8 inches at $10 to $12, yet the $6 to $12 range is presented as the generic answer. It also prices a 2 inch slab, which is below the IRC minimum of 3-1/2 inches and below ACI 330R's statement that there is no benefit in building slabs thinner than that.
• Modernize contradicts itself on one page. Its prose says a 900 square foot slab is $4,500 to $8,000; its table on the same page says $4,500 to $12,600. A 58 percent gap on the ceiling.
• One of these tables is another one, copied. concreteblockcalculator.com reproduces HomeGuide's by-size table row for row on five of its seven rows, including the non-round $860 to $1,700 for a 12 by 12, and interpolates two more rows at exactly $6 and $12. Anyone averaging "the cost guides" on slab size is counting HomeGuide twice.

The sharpest single contradiction is arithmetic you can check without leaving the page it appears on. Barndominium Life prices a 6 inch 30 by 40 slab at $4 to $8 per square foot installed, then lists its own components on the same page: 6 inch concrete $3.57, thickened edges $1.00, vapor barrier $0.50, wire mesh $0.40 and site preparation $0.60 to $1.25. That totals $6.07 to $6.72 per square foot in materials and prep, and then it says labor "can add several dollars per square foot." Its own materials subtotal is 52 percent above the floor of its own installed range and within 16 percent of the ceiling, leaving somewhere between nothing and $1.93 per square foot for the crew.

Where the sources disagree worst

On the same slab, published figures differ by a factor of three. Both numbers are below, because averaging them would hide the finding.

Note that projectcostpro cites HomeGuide as one of its own sources and still lands three times higher on a 10 by 10. The two of them are not measuring the same thing: one is applying a rate, the other is modeling a job.

The two sources that disclose a basis quantity agree with each other. Homewyse computes $10.63 to $13.00 per square foot on a 129 square foot example with a two-hour minimum labor charge, and says the figure is valid to "500 sq ft maximum." Day's 10 by 12, at 120 square feet, is $14.92. An auditable unit-cost model and a working contractor, both disclosing scope, both pricing a slab of about 125 square feet, land within 15 percent of each other at $11 to $15 per square foot. The flat-rate consensus prices that same slab at $6 to $12 and uses the same number for a slab twenty times the size. Homewyse is not the expensive outlier; it is the only aggregator honest enough to say its answer is a small-job price.

For a national figure with a published method rather than a stated range, the SlabCalc Concrete Cost Index is the only one we found: 396 contractor unit-bid records from nine state DOTs plus New York City, adjusted to 2025 dollars, giving a national median of $9.63 per square foot across a $4.96 to $38.00 range. Two disclosures travel with it. Its author also runs a competing concrete calculator site, and DOT flatwork carries traffic control, accessibility detail and often prevailing wage that a residential slab does not. Its median still sits above the ceiling of the range this page used to publish.

What actually moves the number

With figures this time, rather than a list of factors.

What a 6 inch concrete slab costs against a 4 inch one

Thickness is concrete, not labor. Day's Concrete Floors charges $12.50 per square foot at 6 inches and $12.00 at 4, a difference of $0.50, while the extra concrete alone costs him $0.93 to $1.18 at his own supplier's rates. He charges less for the extra two inches than it costs him. On his 30 by 30 page he says it outright: dropping from 6 inches to 4 saves 5.5 cubic yards, "so you could deduct $880 dollars," which is $0.98 per square foot and 100 percent material. No source publishes a labor premium for a thicker slab. HomeGuide's by-thickness table adds a flat $2 per square foot per 2 inches, roughly double the concrete delta. How thick a slab should be has the structural side, and the arithmetic is simple: a cubic yard covers 81 square feet at 4 inches, 65 at 5 and 54 at 6.

Priced at our $160 per cubic yard delivered default, going from 4 inches to 6 costs $0.98 to $0.99 per square foot in concrete, at every size, because the ratio does not change: a 10x10 goes from $198 to $296, a 20x20 from $790 to $1,185, a 30x40 from $2,370 to $3,556. That is the figure to check a quote against. It also happens to be the same number the contractor arrived at independently, since his $880 deduction on a 900 square foot slab works out at $158 per cubic yard, within a couple of dollars of the delivered rate we default to. So a 6 inch slab should cost about a dollar a square foot more than the 4 inch version and no more, and if a quote adds two or three dollars for the extra two inches, the extra is margin rather than material.

Reinforcement is cheaper than the aggregators say, and one figure is wrong by a factor of twenty. Homewyse prices 6 by 6 welded wire mesh installed at $0.83 to $0.98 per square foot on a 534 square foot basis. Day's prices the mesh material at $0.36 to $0.52 and charges $0.75 per square foot to switch from fiber to mesh. Against those, HomeGuide's $1.40 to $4.00 for rebar and Angi's $0.50 to $1.00 bracket reality loosely. But Angi prices fiber mesh at $2 to $3 per square foot, and fiber is an admixture: a contractor publishes his supplier's rate at $7.50 to $8.00 per cubic yard at the manufacturer's dosage of 1 to 1.5 lb per yard, and a cubic yard covers 81 square feet at 4 inches, so fiber is about $0.09 to $0.10 per square foot. Angi's figure is twenty to thirty times the real cost, and the tell is on its own page: it prices rebar cheaper than its own fiber figure, which is backwards, because fiber is the budget option. Day's own itemization confirms the direction at $0.13 for fiber against $0.36 for mesh. Rebar, mesh and vapor barrier covers which to use, and the rebar calculator prices a grid from current bar prices.

Vapor barrier. Since the 2021 IRC the requirement, where it applies, is 10 mil meeting ASTM E1745 Class A with 6 inch laps, not the 6 mil poly older editions allowed. Material runs $0.15 to $0.38 per square foot for 10 mil Class A and $0.22 to $0.67 for 15 mil across five suppliers; installed is around $0.50. Non-compliant 6 mil construction poly is $0.06. Under-slab insulation and vapor barriers has the full comparison, including that the same 10 mil roll is 26 percent more at one supplier than another.

Finish. HomeGuide prices a broom finish specifically at $6 to $13 per square foot and exposed aggregate at $7 to $18, calling the difference "approximately $2 to $3 per square foot more than plain concrete." Stamped roughly doubles a plain slab and has its own page. One gap worth stating: nobody prices a steel-trowelled interior finish differently from a broom finish. We searched for it twice, from different angles, and broom against hard trowel is never itemized as two priced lines anywhere.

Pumping and access. A line pump runs $150 to $250 an hour and a boom pump $200 to $300 or more, with minimums covering the first two to four hours; one contractor simply adds a flat $1,500. Ready-mix delivery has the fee schedule, including waiting time at 5 to 7 minutes per yard and then $2 to $5 a minute.

Labor, and how much of the bill it is. The Bureau of Labor Statistics puts cement masons and concrete finishers at a median of $27.41 an hour nationally with a 90th percentile of $41.10, and Craftsman's estimating manual puts a cement mason's fully burdened cost at $35.34 with the burden disclosed at 22.92 percent for insurance and employer taxes. A four-person crew at loaded rates is $1,320 to $2,160 a day, and the one published productivity example we could find is 600 square feet per crew-day, which works out at $2.20 to $3.60 per square foot. That brackets Day's implied $4.33 at a 20 by 20 and the $3 to $5 HomeGuide publishes. On labor's share of the bill, every source except one agrees it is the majority: 70 to 79 percent on stamped work, 78 percent in one worked example, 56 percent in Day's own 40 by 24 itemization. HomeGuide's slab page is the only source in this topic claiming materials are the majority, and it contradicts itself one page over, where it puts labor at 67 to 71 percent.

Doing it yourself

The material is the small part, which is the whole reason the labor question matters. On a 20 by 20 slab at 4 inches the ready-mix is about $790 at our $160 per yard list default, or $938 once the short load fee goes on, against an installed figure of $2,400 to $4,800. Add forms, mesh, a vapor barrier and a base and you are still well under half the quoted price in materials.

What you are taking on is a job with a clock. Once the truck starts discharging you have the length of one pour to screed, float, edge, joint and finish, and four separate state specifications put the maximum gap between truckloads at thirty minutes before you get a cold joint. A 20 by 20 slab is about five cubic yards, which is one truck and manageable. A 30 by 40 is nearly fifteen, which is two or three loads and a crew you do not have. How to pour a concrete slab walks the sequence, and the yardage calculator has the cold joint window and why coming up short is the expensive mistake.

Bags are not the answer above about half a yard. Forty-five 80 lb bags make one cubic yard, so a 20 by 20 slab is 223 bags, and bags per yard has the crossover arithmetic.

Estimate your own slab

The slab cost calculator itemizes material, delivery and finishing labor from your dimensions with every price editable. One thing to know before you trust it on a small slab: it applies no minimum job charge, so under about 400 square feet it reads low against what a contractor will actually quote. Compare its output against the $1250 labor minimum in the first section and take the higher number.

For other shapes and jobs: the slab calculator for volume, reinforcement and base; pad cost for anything under a yard, where the short load penalty dominates; driveway cost; patio cost; slab foundations for a monolithic slab with a thickened edge; and a slab for a metal building, which is a different problem because of the column loads.