Concrete Slab Cost Calculator
Concrete slab cost calculator for a patio, garage floor or shed pad. Prices ready mix, base, forms, reinforcement, finishing and control joints as line items.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Installed cost range
- $2,700 to $4,500
- 400 sq ft at 4 in thick, patio, broom finish
- Cost per square foot
- $7 to $11 per sq ft
- Contractors quote flatwork this way, so this is the number to compare bids against
- Concrete to order
- 5.33 cu yd
- 5.5 cu yd ordered to the quarter yard including 8% waste. Over the short load threshold, so no small order fee
- Ready mix delivered
- $1,038 to $1,113
- 5.5 cu yd at $175 per cu yd plus $75 to $150 delivery
- Bag mix instead
- 241 bags of 80 lb, $1,326 to $1,808
- More expensive than a truck here. Bags only win under about 2 cubic yards, and every bag is mixed by hand
- Materials
- $1,471 to $1,938
- Concrete, 6.9 tons of base stone, 80 ft of forms, mesh reinforcement
- Labor
- $1,260 to $2,520
- Placing and finishing
- Control joints
- 40 ft of cuts
- Cut within 10 ft each way, a quarter of the slab depth deep, within 12 hours of the pour
- Concrete strength to specify
- 3,500 psi air entrained where winters are severe
- Flatwork that will not be enclosed and heated is exempt from the vapor retarder under IRC R506.2.3
- Planning estimate only
- Get two local quotes
- Ready mix price, labor rates and disposal vary more by metro area than by any input on this page
Concrete Slab Cost formula
Concrete = Length x Width x Thickness / 12, plus 8% waste, ordered to the quarter cubic yard
Short load fee = (4 cu yd minimum - Yards ordered) x $40 to $80, when the order is under a full load
Base stone = Area x Base depth / 12 / 27 x 1.4 tons per cubic yard
Joint spacing in feet = Slab thickness in inches x 24 to 36 / 12
Total = Concrete + Base + Forms + Vapor retarder + Reinforcement + Labor + Finish adder + Saw cuttingWorked example
A 12 x 24 ft garage floor, 5 in thick, on a 6 in base, with a rebar grid, a smooth trowel finish and a pump truck because the truck cannot get behind the house.
The slab is 288 sq ft and holds 120 cubic feet of concrete, which rounds to 5 cubic yards ordered after waste, so it clears the short load threshold. Ready mix runs $950 to $1,025 delivered. The 6 in base takes 7.5 tons of stone. Rebar at $0.70 to $1.40 a square foot adds $202 to $403. Labor is $1,926 to $3,652, and $900 to $1,600 of that is the pump alone. The slab lands near $3,400 to $5,700, or $12 to $20 per square foot. The pump is a quarter of the low end, which is why access is worth solving before you price the concrete.
Quick reference
| Line item | Basis | Typical range |
|---|---|---|
| Ready mix concrete | Per cubic yard delivered | $150 to $220 |
| Delivery charge | Per load | $75 to $150 |
| Short load fee | Per cubic yard under about 4 | $40 to $80 |
| 80 lb bag mix | Per bag, yields 0.6 cu ft | $5.50 to $7.50 |
| Crushed stone base | Per ton delivered | $28 to $50 |
| Forms, lumber and stakes | Per linear foot of perimeter | $1.50 to $3.00 |
| Welded wire mesh | Per sq ft of slab | $0.30 to $0.60 |
| Rebar grid, No. 4 at 18 in | Per sq ft of slab | $0.70 to $1.40 |
| Placing and finishing labor | Per sq ft | $3.00 to $6.00 |
| Stamped and colored adder | Per sq ft over broom | $8.00 to $14.00 |
| Pump truck | Minimum charge | $900 to $1,600 |
| Saw cut control joints | Per linear foot | $1.50 to $3.00 |
The fees are why a small slab costs so much per square foot
Concrete is priced by the cubic yard, but a residential slab rarely orders a full load. Suppliers set a delivery charge and then add a short load fee for every yard below about four, because the truck and driver cost the same whether they carry two yards or ten. On a 2 cubic yard pour those two fees can exceed the concrete itself.
That is the whole reason bag mix competes at small sizes. Forty five 80 lb bags make a cubic yard, and at $5.50 to $7.50 a bag that is $250 to $340 with no delivery and no fee. Under about two cubic yards the bags win on money. Above it the truck wins, and the gap opens fast, because mixing 90 bags by hand is a day of work and a cold joint risk every time the mixer runs dry.
Base, joints and finish decide whether the slab lasts
Three line items carry most of the durability and none of them are the concrete. The compacted base spreads the load so the slab is not bridging soft spots in the subgrade, and IRC R506.2.2 asks for 4 inches of clean graded stone under a slab on grade. Skipping it saves a few hundred dollars and buys settlement cracks.
Control joints decide where the slab cracks, because it will crack. The American Concrete Institute puts spacing at 24 to 36 times the slab thickness, so a 4 inch slab gets a joint every 8 to 12 feet, cut a quarter of the depth deep within about 12 hours of the pour. The finish decides how it behaves in use: a broom finish has real texture and stays walkable wet, while a steel troweled surface belongs inside where it will not ice over.
What this calculator leaves out
Excavation, tree root or stump removal, hauling spoil, and any fill needed to bring a low site up to grade. It does not price demolition and disposal of an existing slab, a thickened edge or turndown footing where the slab carries a wall, frost footings in a cold climate, radiant tubing, a moisture mitigation coating over a slab that already failed a moisture test, or a subslab drain. Permit fees, sealing and the cost of matching an existing color also sit outside it. A driveway is a different job with its own thickness and reinforcement rules, and a slab that carries a building needs a foundation design rather than these numbers.
Code limits that apply
- IRC R506.1
Concrete floor slabs on grade are at least 3.5 in thick
If you miss it: A thin slab poured to stretch the yardage cracks through under the first vehicle or heavy load
- IRC R506.2.2
A 4 in base course of clean graded gravel or crushed stone, except on well drained Group I soils
If you miss it: A slab poured straight on clay settles unevenly and cracks along the soft spots
- IRC R506.2.3
A Class I vapor retarder between the base and the slab, lapped 6 in, under heated interior floors
If you miss it: Ground moisture wicks up and lifts the flooring glued to the slab months later
- IRC Table R402.2
3,500 psi air entrained concrete for garage floors, porches and steps in a severe weathering region
If you miss it: Non air entrained mix in a freeze thaw climate scales and spalls within a few winters
- ACI 302.1R
Control joint spacing 24 to 36 times the slab thickness, cut a quarter of the depth deep
If you miss it: Joints cut late or too shallow do not control the crack, and the slab cracks where it wants to
- IRC R105.2
A slab that is part of a building or an accessory structure over 200 sq ft is not permit exempt
If you miss it: Unpermitted work has to be exposed for inspection or removed when it surfaces at sale
Rows marked checked produce a warning in the results when an entry crosses the limit. The others are on the plans or on site and this calculator does not test them. Local amendments can be stricter; the adopted edition and the inspector govern.
Mistakes that cost money
- Pricing concrete by the cubic yard alone. On a small residential pour the delivery and short load fees can be a third of the concrete bill.
- Laying wire mesh on the ground and pouring over it. Mesh has to sit near mid depth on chairs or it reinforces nothing.
- Skipping the compacted base on clay. The slab bridges the soft spots until it does not, and the crack follows the weak subgrade.
- Cutting control joints late. They go in within 12 hours, a quarter of the slab depth deep, or the slab picks its own crack lines first.
- Troweling an outdoor slab smooth. A steel troweled surface is dangerous wet and seals the surface so it cannot release bleed water.
- Forgetting site access. A pump truck adds $900 to $1,600 and is decided by whether a loaded mixer can get within about 18 ft of the forms.
Key facts
- A 20 by 20 ft concrete patio slab 4 in thick typically costs $2,700 to $4,500 installed, which is $7 to $11 per square foot.
- Ready mix concrete typically runs $150 to $220 per cubic yard delivered in 2026, plus a $75 to $150 delivery charge.
- Suppliers usually add a short load fee of $40 to $80 per cubic yard on any order under about 4 cubic yards.
- An 80 lb bag of concrete mix yields 0.6 cubic feet, so a cubic yard takes 45 bags and bag mix only beats a truck under about 2 cubic yards.
- IRC R506.1 sets the minimum slab thickness at 3.5 in, and IRC R506.2.2 asks for a 4 in base course of clean graded gravel or crushed stone.
- The American Concrete Institute puts control joint spacing at 24 to 36 times the slab thickness, so a 4 in slab gets joints every 8 to 12 ft.
Frequently asked questions
How much does a 20x20 concrete slab cost?
About $2,700 to $4,500 installed for a 4 in patio slab on a 4 in base with wire mesh and a broom finish, which is $7 to $11 per square foot. A garage floor at 5 or 6 in with rebar runs higher.
Is it cheaper to pour concrete yourself or order a truck?
Bags win under about 2 cubic yards, where the delivery and short load fees dominate a small order. Above that a truck is cheaper and far better concrete, because 90 bags mixed by hand invites cold joints.
How thick should a concrete slab be?
IRC R506.1 sets 3.5 in as the minimum. Use 4 in for patios, walks and shed pads, and 5 to 6 in with rebar for a garage floor, a driveway apron or anything a vehicle parks on.
How far apart do control joints go in a slab?
The American Concrete Institute puts spacing at 24 to 36 times the slab thickness, so a 4 in slab gets joints every 8 to 12 ft. Cut them a quarter of the slab depth deep within about 12 hours of the pour.
Sources and references
- Chapter 5 Floors, slab thickness, base course and vapor retarder, 2021 IRC (ICC)
- Chapter 4 Foundations, Table R402.2 minimum specified compressive strength (ICC)
- Joints in concrete slabs on ground (American Concrete Institute)
- Slabs on ground: design, placing and finishing (American Concrete Institute)
Next steps for this project
The usual order for a concrete & masonry project. See all concrete & masonry calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.