Concrete Slab Cost Calculator
Every line of a slab — mix, short-load fee, base, forms, steel, labor and finish.
Estimated slab cost
$3,186.74
- Area
- 400 sq ft at 4.0 in
- Concrete to order
- 5.43 yd³ (4.94 yd³ net)
- Ready-mix
- $894.81
- Gravel base
- $222.22 (4.94 yd³)
- Forms
- $240.00
- Mesh / rebar
- $140.00
- Labor
- $1,400.00
- Subtotal
- $2,897.04
- Contingency (10%)
- $289.70
- Cost per square foot
- $7.97/sq ft
- Bagged equivalent
- 245 × 80 lb bags
Estimates only — plant pricing, minimum loads and short-load fees vary by supplier and by how far you are from the batch plant. Get the fee schedule in writing before booking a small pour.
Pricing the base stone separately? Use the gravel calculator →
How this is calculated
concrete = area × thickness(in)/12 / 27 × (1 + waste%) short fee = max(minimum load − concrete, 0) × fee per yd³ base = area × base depth(in)/12 / 27 × stone price forms = perimeter × rate per linear ft steel = area × rate per sq ft labor = area × rate per sq ft total = (all lines) × (1 + contingency%)
The short-load fee is charged on the gap between your order and the plant minimum, which produces a counter-intuitive result worth checking on small pours: because you are already paying for the yards you skipped, ordering up to the minimum costs only the difference between the mix price and the fee. A slab short by two yards on a $60 fee can often be made thicker for very little extra.
Where the money goes on a typical slab
| Line | Typical share | Notes |
|---|---|---|
| Ready-mix concrete | 25-35% | $120-$200 per cubic yard delivered |
| Pour & finish labor | 25-40% | $2.50-$5.00 per sq ft, broom finish |
| Gravel base | 8-15% | 4-6 in compacted under the slab |
| Forms | 5-10% | $2-$5 per linear foot of edge |
| Mesh or rebar | 3-8% | Mesh $0.20-$0.50, rebar grid $0.80-$1.60/sq ft |
| Short-load fee | 0-20% | Only on pours under the plant minimum |
| Pump | 0-15% | $700-$1,200 when the truck cannot reach |
Common slab sizes at 4 inches
| Slab | Area | Concrete | 80 lb bags |
|---|---|---|---|
| 10 × 10 | 100 sq ft | 1.23 yd³ | 56 |
| 10 × 12 | 120 sq ft | 1.48 yd³ | 67 |
| 12 × 12 | 144 sq ft | 1.78 yd³ | 80 |
| 16 × 20 | 320 sq ft | 3.95 yd³ | 178 |
| 20 × 20 | 400 sq ft | 4.94 yd³ | 223 |
| 24 × 24 | 576 sq ft | 7.11 yd³ | 320 |
| 30 × 40 | 1,200 sq ft | 14.81 yd³ | 667 |
Volumes are net, before any waste allowance, and bag counts assume 0.6 cubic feet per 80 lb bag. Note how quickly bags stop being reasonable — even a 10 by 12 pad is 67 bags, which is most of a day of mixing and a pour that sets in stages rather than as one slab.
Frequently asked questions
How much does a concrete slab cost?
Most residential slabs land between $6 and $12 per square foot installed, so a 20 by 20 pad runs roughly $2,400 to $4,800. The concrete itself is only about a third of that — base preparation, forms, reinforcement and finishing labor make up the rest, which is why quotes vary so much more than the price of the mix does.
What is a short-load fee?
A surcharge ready-mix plants add when you order less than their minimum, commonly four to five cubic yards. It typically runs $60 to $150 for each yard you are short, because the truck, the driver and the trip cost the same whether it arrives full or a third full. On a small pad this single line can exceed the price of the concrete.
Is it cheaper to use bags or ready-mix?
Bags win only on genuinely small pours. An 80 lb bag yields 0.6 cubic feet, so one cubic yard takes 45 bags — around $250 in material plus a great deal of mixing. Ready-mix beats that on price per yard immediately, but the delivery and short-load fees mean the crossover usually sits somewhere between one and two cubic yards.
How thick should a concrete slab be?
Four inches for patios, walkways and most shed pads; five to six for driveways and anything a vehicle parks on; six or more with reinforcement for heavy equipment. Going from four to six inches raises the concrete volume by half, so it is one of the biggest single levers on the total.
Do I need rebar or wire mesh?
Mesh is the usual choice for a four inch residential slab and costs a fraction of rebar. Rebar makes sense for thicker slabs, poor soil, or anything carrying vehicle loads. Neither prevents cracking — they hold the crack tight once it happens, which is what keeps a slab serviceable rather than pretty.
What does stamped or coloured concrete add?
Usually $6 to $12 per square foot on top of a plain broom finish, often doubling the total. The work is in the release agents, stamping, sealing and the extra hands needed before the pour sets, not in the material — which is why the surcharge is quoted per square foot rather than per yard.
Results are planning estimates and not structural or engineering advice. Slab thickness, reinforcement, subgrade preparation and footings for anything load-bearing are governed by local code and soil conditions — get a written quote and check permit requirements before pouring.