A ready-mix truck pouring concrete into a slab form

Concrete cost calculator

A 12 × 20 ft slab 4 in thick, with a #4 rebar grid, a 4 in gravel base and form boards, comes to about $860 in materials at the default prices ($3.59 a square foot) before delivery fees, base gravel, boards and labor, which take your own prices.

Reinforcement, base and forms optional
Your plans or local code set the spacing.
Prices used for the cost estimate
$
For #4 bar, 20 ft. Online listings in November 2026: $9.22 to $18.77 at 7 stores.
$
Quarries averaged $16.78 a ton for crushed stone in 2025 (USGS), before delivery.
$
$
The 2023 national average (NRMCA), carried to September 2026 by the BLS price index. Use your plant's quote.
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Ask your plant. Small loads often carry a surcharge.
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Online listings in November 2026: $5.56 to $7.59 at 7 stores.
%
$
Only when the truck can't reach the forms; ask your plant or a pump company.
$
For a contractor to place and finish; leave blank if you are doing it yourself. City bids in 2025 put 4 in concrete at a typical $10.02 a sq ft installed, of which about $7.66 is not the concrete.
$860 materials total
$3.59 per sq ft
3.26 cubic yards

What to order Order 3.5 cu yd of ready-mix, or buy 147 bags of 80 lb concrete mix. Also buy 22 #4 bars of 20 ft, 6 tons of base gravel and 8 boards of 2x6, 8 ft long.

Cost estimate

Ready-mix: 3.5 cu yd × $174.00$609.00
Bags: 147 × $6.47$951.09
Rebar: 22 × $11.43$251.46
Total with ready-mix$860.46
Total with bags$1,202.55

At NRMCA's 2023 range of average ready-mix prices carried to today, the total with ready-mix would be $822 to $902.

Add a labor price per square foot under Prices for an installed estimate.

Plants often charge for delivery and add a fee to small loads; enter your plant's fees under Prices to compare fairly.

All quantities and the working
#4 rebar14 bars of 11.5 ft and 8 of 19.5 ft: 317 linear ft, 212 lb, 112 ties
Gravel base2.96 cu yd compacted: 5.63 tons of crusher run at 1.9 tons per compacted yard
Form boards64 ft around the edge: 8 boards of 2x6, 8 ft long (a 2x6 is 5.5 in wide)
Volume80 cu ft (2.96 cu yd, 2.265 m³)
With 10% extra88 cu ft (3.26 cu yd)
Ready-mix to order3.5 cu yd (rounded up to the next ¼ yard)
40 lb bags294 (0.3 cu ft each)
50 lb bags235 (0.375 cu ft each)
60 lb bags196 (0.45 cu ft each)
80 lb bags147 (0.6 cu ft each)
90 lb bags131 (0.675 cu ft each)
Weight of the concreteabout 12,760 lb (6.38 tons)

How it was worked out

12 ft × 20 ft × 4 in = 80 cu ft

80 cu ft ÷ 27 = 2.96 cu yd

What goes into the budget

  • Concrete. Ready-mix starts at $174 a cubic yard: NRMCA's 2023 national average carried to September 2026 by the BLS price index (see concrete price per yard). Bags start at $6.47 for 80 lb, the typical online price in November 2026. Both are compared, and the cheaper total counts.
  • Delivery and small-load fees, and a pump. These vary by plant and site, so they start empty. Ask your plant; concrete delivery cost shows the short-load and standby terms four plants published in 2025.
  • Reinforcement. A rebar grid counts bars, linear feet, weight and ties; #4 bar starts at $11.43 for 20 ft ($9.22 to $18.77 across 7 store listings). Welded wire mesh counts sheets or rolls with an allowance for laps.
  • Gravel base. Compacted crusher run at 1.9 tons per cubic yard, the middle of Wisconsin DOT's range; enter your supplier's price per ton.
  • Forms. The perimeter in 8 ft boards, with the narrowest board at least as wide as the slab is thick.
  • Labor. Your contractor's price per square foot, if you are hiring the pour and finish. For what cities paid contractors in 2025, installed, see the costs of a concrete patio, a concrete driveway and a sidewalk.

Sales tax applies at the rate you enter. The answer shows every line, so you can see what drives the total and compare it with a contractor's quote.

Concrete cost for common slabs

Concrete only, before delivery fees, reinforcement, base, forms and labor
4 in slabSq ftReady-mix (10% extra, rounded to ¼ yd)80 lb bags (10% extra)Ready-mix per sq ft
10 × 10 ft100$261.00$401.14$2.61
12 × 12 ft144$348.00$569.36$2.42
12 × 20 ft240$609.00$951.09$2.54
16 × 20 ft320$783.00$1,268.12$2.45
20 × 20 ft400$957.00$1,585.15$2.39
24 × 24 ft576$1,392.00$2,277.44$2.42

If a contractor quotes an installed price per square foot that includes materials, compare it with the materials total here: the difference is roughly what their labor and overhead cost. If they quote labor alone, enter it under Prices.

Sources