Concrete Slab Cost Calculator
Budget a concrete slab line by line — ready-mix, gravel base, rebar, forms, labour and contingency — with every unit price left as an input you set locally.
Concrete Slab Cost Calculator: with the default inputs, estimated total cost is $3,811.
4 in for patios and walkways, 5–6 in for driveways and anything carrying vehicles.
Regional and volatile — call a local plant for a quote. The default is a placeholder to make the example work, not a market price.
Uneven subgrade, spillage and a slightly deep form all eat concrete. 5–10% is normal; order in quarter-yard increments.
Plants usually charge a short-load fee under 3–4 cubic yards and may bill for time on site. Ask when you get the quote.
Compacted crushed stone under the slab. Zero if you are pouring on prepared subgrade.
Delivered price per US short ton. Another local figure — the default is a placeholder.
Reinforcement does not stop concrete cracking — it holds the crack together. Most codes want rebar in anything carrying a vehicle.
#4 (½ in) bar. Add tie wire and chairs — a few dollars either way.
Wildly regional — from under $2/ft² in low-cost rural markets to well over $8 in expensive metros. Get a quote and put it here.
Broom finish is included in the labour rate. Stamped, coloured, polished or exposed-aggregate work costs more per square foot — enter the difference.
The sum of every line below, plus contingency.
- Cost per square foot
- $9.53
- Slab area
- 400Square feet.
- Concrete to order
- 5.43Cubic yards including the waste allowance — round up to the next quarter yard when you order.
- Ready-mix, delivered
- $951
- Crushed stone
- 7.16US short tons.
- Gravel base
- $322
- Reinforcement
- $392
- 20 ft rebar sticks to buy
- 28
- Forms
- $200
- Labour and finishing
- $1,600
- Materials subtotal
- $1,865
- Contingency
- $346
Assumptions
- Every unit price is your input. No material or labour price is sourced or assumed to be current — the defaults are placeholders chosen to make the worked example run, and they should be replaced with local quotes.
- Compacted crushed stone base at 1.45 US short tons per cubic yard, the same density figure the gravel calculator on this site uses.
- Rebar is #4 bar in a square grid at the spacing you select, priced in 20 ft sticks and rounded up to whole sticks. Tie wire, chairs and lap allowance are not counted.
- Concrete volume is a plain rectangular prism plus your waste allowance. Thickened edges, footings, haunches and slope are not modelled and will need more concrete.
- Labour is a flat rate per square foot covering placing and a broom finish; the decorative surcharge is added on top. Real bids do not scale linearly — small slabs cost more per foot and large ones less.
- Not included: permits, inspection, concrete pumping, curing compound or sealer, expansion joint material, spoil disposal, or reinforcement chairs and dowels.
- Ready-mix concrete$95125%
- Gravel base$3228%
- Reinforcement$39210%
- Forms & barrier$2005%
- Labour & finishing$1,60042%
- Contingency$3469%
| Item | Quantity | Cost | Share of total |
|---|---|---|---|
| Ready-mix concrete, delivered | 5.43 yd³ | $951 | 24.9% |
| Compacted crushed stone base | 7.16 tons | $322 | 8.5% |
| #4 rebar grid at 18 in centres | 28 sticks (560 lin ft) | $392 | 10.3% |
| Forms | 80 lin ft | $200 | 5.2% |
| Vapour barrier | — | $0 | 0% |
| Excavation and site prep | — | $0 | 0% |
| Labour, placing and finishing | 400 ft² | $1,600 | 42% |
| Contingency | 10% | $346 | 9.1% |
| Total | 400 ft² | $3,811 | 100% |
| Slab | Area (ft²) | Concrete (yd³) | Estimated total |
|---|---|---|---|
| 10 × 10 patio | 100 | 1.36 | $1,008 |
| 12 × 20 single driveway | 240 | 3.26 | $2,349 |
| 20 × 20 two-car pad | 400 | 5.43 | $3,811 |
| 24 × 24 garage | 576 | 7.82 | $5,446 |
| 30 × 40 shop floor | 1,200 | 16.3 | $11,144 |
Uses your thickness, base depth, reinforcement and unit prices — only the footprint changes.
How this is worked out
The formula
Area = length × width
Volume (yd³) = area × thickness ÷ 12 ÷ 27, × (1 + waste allowance)
Base (tons) = area × base depth ÷ 12 ÷ 27 × 1.45 tons per cubic yard
Rebar grid: bars one way = floor(width ÷ spacing) + 1, each the length of the slab
bars the other way = floor(length ÷ spacing) + 1, each the width of the slab
sticks to buy = ceiling(total linear feet ÷ 20)
Total = ready-mix + delivery + base + reinforcement + forms + vapour barrier
+ excavation + (area × labour rate) then × (1 + contingency)Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Slab length
- A number.in ft, in, m, yd · 0 or more · defaults to 20
- Slab width
- A number.in ft, in, m, yd · 0 or more · defaults to 20
- Slab thickness
- 4 in for patios and walkways, 5–6 in for driveways and anything carrying vehicles.in in, ft, cm, mm · 0 or more · defaults to 4
- Ready-mix price per cubic yard
- Regional and volatile — call a local plant for a quote. The default is a placeholder to make the example work, not a market price.in dollars · 0 or more · defaults to 175
- Waste and over-excavation allowance
- Uneven subgrade, spillage and a slightly deep form all eat concrete. 5–10% is normal; order in quarter-yard increments.a percentage · from 0 to 50 · defaults to 10
- Delivery and short-load fees
- Plants usually charge a short-load fee under 3–4 cubic yards and may bill for time on site. Ask when you get the quote.in dollars · 0 or more · defaults to 0
- Gravel base depth
- Compacted crushed stone under the slab. Zero if you are pouring on prepared subgrade.in in, cm, ft · 0 or more · defaults to 4
- Crushed stone price per ton
- Delivered price per US short ton. Another local figure — the default is a placeholder.in dollars · 0 or more · defaults to 45
- Reinforcement
- Reinforcement does not stop concrete cracking — it holds the crack together. Most codes want rebar in anything carrying a vehicle.None — plain concrete · Welded wire mesh (6×6 W1.4) · #4 rebar grid at 18 in centres · #4 rebar grid at 24 in centres · #4 rebar grid at 12 in centres
- Rebar price per 20 ft stick
- #4 (½ in) bar. Add tie wire and chairs — a few dollars either way.in dollars · 0 or more · defaults to 14
- Wire mesh price per square foot
- A number.in dollars · 0 or more · defaults to 0.35
- Labour, placing and finishing
- Wildly regional — from under $2/ft² in low-cost rural markets to well over $8 in expensive metros. Get a quote and put it here.in dollars · 0 or more · defaults to 4
- Decorative finish surcharge
- Broom finish is included in the labour rate. Stamped, coloured, polished or exposed-aggregate work costs more per square foot — enter the difference.in dollars · 0 or more · defaults to 0
- Forming cost per linear foot(under More options)
- Lumber, stakes and the labour to set them, around the perimeter.in dollars · 0 or more · defaults to 2.5
- Vapour barrier price per square foot(under More options)
- 6-mil polyethylene under the slab. Required under most interior slabs, optional outdoors. Zero to skip.in dollars · 0 or more · defaults to 0
- Excavation and site prep(under More options)
- Machine hire, spoil removal, tree roots — whatever it takes to get to a flat, compacted subgrade.in dollars · 0 or more · defaults to 0
- Contingency(under More options)
- Slabs uncover surprises. 10% on a straightforward pour, more on anything with access problems.a percentage · from 0 to 50 · defaults to 10
What you get back
- Estimated total costmain answer
- The sum of every line below, plus contingency.
- Cost per square foot
- Slab area
- Square feet.
- Concrete to order
- Cubic yards including the waste allowance — round up to the next quarter yard when you order.
- Ready-mix, delivered
- Crushed stone
- US short tons.
- Gravel base
- Reinforcement
- 20 ft rebar sticks to buy
- Forms
- Labour and finishing
- Materials subtotal
- Contingency
What this assumes
- Every unit price is your input. No material or labour price is sourced or assumed to be current — the defaults are placeholders chosen to make the worked example run, and they should be replaced with local quotes.
- Compacted crushed stone base at 1.45 US short tons per cubic yard, the same density figure the gravel calculator on this site uses.
- Rebar is #4 bar in a square grid at the spacing you select, priced in 20 ft sticks and rounded up to whole sticks. Tie wire, chairs and lap allowance are not counted.
- Concrete volume is a plain rectangular prism plus your waste allowance. Thickened edges, footings, haunches and slope are not modelled and will need more concrete.
- Labour is a flat rate per square foot covering placing and a broom finish; the decorative surcharge is added on top. Real bids do not scale linearly — small slabs cost more per foot and large ones less.
- Not included: permits, inspection, concrete pumping, curing compound or sealer, expansion joint material, spoil disposal, or reinforcement chairs and dowels.
About this calculator
A concrete slab is one of the few home projects where the material is the cheap part. On a typical 20 × 20 ft pad the concrete itself is often a third of the bill and labour is close to half — which is why a national "cost per square foot" figure is worthless to you. This calculator does not invent one. Every unit price is a field you fill in, so the estimate is as good as the quotes you put into it.
Get three numbers before you start
- Ready-mix, per cubic yard, delivered. Call the plant. Ask about the short-load fee, because under 3 or 4 yards almost everyone charges one, and ask how long the truck can sit before per-minute charges start.
- Crushed stone, per ton, delivered. Cheap material, expensive freight — the price is mostly how far the quarry is from you.
- Placing and finishing labour, per square foot. This is the one that ranges from under $2 to well over $8 depending on the market, and it is the single biggest driver of the total.
The defaults on this page exist so the example runs. They are placeholders. Replace them.
What the slab actually needs
Thickness. 4 inches for a patio or walkway. 5 to 6 inches, with rebar, for anything a vehicle drives or parks on. Going from 4 to 6 inches raises the concrete volume by half but rarely raises the total by more than about 15%, because the labour and base do not change — which makes it one of the better-value upgrades on the list.
Base. Four inches of compacted crushed stone under the slab gives it something uniform to sit on and lets water drain away instead of freezing under it. On soft or clay soil it matters more than the concrete grade.
Reinforcement. Worth being clear about: reinforcement does not stop concrete from cracking. Concrete shrinks as it cures and it will crack somewhere. What rebar does is hold the two sides of that crack in the same plane so the slab stays flat and keeps carrying load. Control joints — cut within 6 to 18 hours, about a quarter of the slab depth, spaced in feet at roughly two to three times the thickness in inches — are what decide where it cracks. Skipping them is the most common reason a slab looks bad in year two.
What is not in here
Permits and inspection, pumping if the truck cannot reach the forms, curing compound or sealer, expansion joint material, and hauling away whatever you dug out. Any of them can add several hundred dollars. The contingency field exists because slabs uncover surprises — a buried stump, a soft spot, rain the night before the pour. Ten percent on a straightforward pour, more if access is awkward.
Frequently asked questions
▸How much does a concrete slab cost per square foot?
There is no honest national answer, which is why this calculator asks for your local prices instead of assuming one. Concrete is usually about a third of the bill and labour close to half, and labour ranges from under $2 to over $8 a square foot depending on the market. Get quotes and put them in.
▸How thick should a concrete slab be?
4 inches for patios, walkways and sheds. 5 to 6 inches with rebar for driveways, garages and anything carrying a vehicle. Going from 4 to 6 inches usually adds well under 20% to the total because only the concrete volume changes.
▸Do I need rebar in a concrete slab?
For anything a vehicle uses, yes, and most codes require it. Reinforcement does not prevent cracks — shrinkage guarantees them — but it keeps the two sides of a crack aligned so the slab stays flat and keeps carrying load.
▸How much concrete do I need for a 20 × 20 slab?
At 4 inches thick, 400 square feet works out to 4.94 cubic yards before waste, so about 5.4 yards with a 10% allowance. Order in quarter-yard increments and round up — running short mid-pour is far worse than buying a little extra.
▸Is bagged concrete cheaper than ready-mix?
Only for very small pours. Roughly 45 eighty-pound bags make a cubic yard, so anything over about a yard is usually cheaper delivered — even after the short-load fee — and vastly less work.
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