Common-size reference
Concrete Slab Cost by Common Size
Last reviewed September 6, 2026
Multiply slab area by a quoted installed rate, then add excluded work and fixed charges. The table demonstrates costs at hypothetical $8, $12, and $16 per ft²; these are calculation scenarios, not local quotes or national averages.
Use the related calculator →Reference table
Slab costs at explicit example installed rates
Hypothetical rates for arithmetic only. Replace them with equivalent local scopes. Removal, finish upgrades, and fixed charges are excluded.
| Slab size | Area | At $8/ft² | At $12/ft² | At $16/ft² |
|---|---|---|---|---|
| 8×8 ft | 64 ft² | $512 | $768 | $1,024 |
| 10×10 ft | 100 ft² | $800 | $1,200 | $1,600 |
| 12×12 ft | 144 ft² | $1,152 | $1,728 | $2,304 |
| 12×16 ft | 192 ft² | $1,536 | $2,304 | $3,072 |
| 16×20 ft | 320 ft² | $2,560 | $3,840 | $5,120 |
| 20×20 ft | 400 ft² | $3,200 | $4,800 | $6,400 |
| 20×24 ft | 480 ft² | $3,840 | $5,760 | $7,680 |
| 24×24 ft | 576 ft² | $4,608 | $6,912 | $9,216 |
| 30×40 ft | 1,200 ft² | $9,600 | $14,400 | $19,200 |
| 40×60 ft | 2,400 ft² | $19,200 | $28,800 | $38,400 |
01
Convert area into a local cost range
Multiply the exact area by current low, typical, and high installed rates for equivalent local scopes. Keep finish, demolition, reinforcement, access, permits, and other extras editable rather than burying them in an unexplained national average.
For a 20×20 ft slab, area is 400 ft². At the hypothetical $12/ft² example rate, the subtotal is $4,800. Adding $600 of genuinely excluded fixed work gives $5,400. This arithmetic does not certify that $12/ft² is available locally.
- Low estimate = area × editable low rate.
- Typical estimate = area × editable typical rate.
- High estimate = area × editable high rate.
- Add fixed charges and project-specific extras separately.
02
What scales and what does not
Concrete volume and many broad-area quantities grow predictably. Mobilization, small-job minimums, difficult access, pump setup, drainage correction, and design work can behave as fixed or nonlinear costs.
03
Check concrete volume separately
The volume table isolates geometry before allowance or supplier rounding. Installed cost rates normally include some material scope; use this quantity as a cross-check rather than charging concrete a second time on top of the installed rate.
- Calculate thickened edges, footings, and piers separately.
- Use the exact formed dimensions.
- Replace presets with dated supplier and contractor inputs.
Limits
What this comparison does not decide
- The cost table uses hypothetical rates; the separate volume table contains geometric quantities before allowance.
- Cost rates should be local, editable, dated, and scoped.
- BLS producer-price indexes track price change; they are not installed retail quotes.
Common questions
Concrete Slab Cost by Common Size FAQ
How much does a 20×20 concrete slab cost?
At hypothetical installed rates of $8, $12, and $16 per ft², its 400 ft² gives subtotals of $3,200, $4,800, and $6,400 before excluded extras. These demonstrate the calculation; obtain a scoped local quote for an actual price.
How much concrete does a 10×10 slab need?
About 1.23 yd³ at 4 inches or 1.85 yd³ at 6 inches, before allowance.
How much concrete does a 20×20 slab need?
About 4.94 yd³ at 4 inches or 7.41 yd³ at 6 inches, before allowance.
Why is my quote higher than area times a rate?
Fixed charges, base work, access, finish, demolition, drainage, and minimums may sit outside a simple area rate.
Should order quantity equal geometric volume?
Usually the estimate should expose a separate allowance and supplier-specific rounding before purchase.