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Volume and bags

Concrete slab calculator

Estimate cubic feet, cubic yards, 80 lb bags, ready-mix cost, labor range, and slab supplies.

Reviewed · May 9, 2026

Home Project Estimates

Concrete slab calculator

May 9, 2026

12 ft by 10 ft slab at 4 in thick.

Concrete volume
1.7 cu yd
44.0 cu ft with 10% waste
80 lb bags
74 bags
Small-job alternative
Slab area
120 sq ft
4 in thickness
DIY material total
$392–$903
Ready-mix plus forms/base
Labor range
$384–$720
Directional slab prep and finish labor
Contractor total
$776–$1,623
Materials plus labor

Shopping list

  • Ready-mix concrete1.7 cu yd
  • Forms, stakes, gravel base, reinforcementProject allowance
  • Finishing tools and curing suppliesAs needed

Assumptions

  • 27 cu ft per cu yd
  • 0.6 cu ft per 80 lb bag
  • 10% waste buffer
  • U.S. near average; pricing data: U.S. near average pricing

Planning estimate only. Not a contractor quote, engineering advice, or permit review.

Project inputs
U.S. near average
Units
ft
ft
in
%
Estimated result

12 ft by 10 ft slab at 4 in thick.

Concrete volume
1.7 cu yd
44.0 cu ft with 10% waste
80 lb bags
74 bags
Small-job alternative
Slab area
120 sq ft
4 in thickness
DIY material total
$392–$903
Ready-mix plus forms/base
Labor range
$384–$720
Directional slab prep and finish labor
Contractor total
$776–$1,623
Materials plus labor
Sub-base, reinforcement, site access, and finishing affect final cost.

Shopping list

  • Ready-mix concrete1.7 cu yd
  • Forms, stakes, gravel base, reinforcementProject allowance
  • Finishing tools and curing suppliesAs needed

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Assumptions in this estimate

  • 27 cu ft per cu yd
  • 0.6 cu ft per 80 lb bag
  • 10% waste buffer
  • U.S. near average; pricing data: U.S. near average pricing

Saved estimates

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How this is calculated

  • Cubic feet are length x width x thickness in feet.
  • Cubic yards divide cubic feet by 27 and round up to the nearest tenth.
  • Bag count uses a typical 0.6 cu ft yield per 80 lb bag.

Assumption register

Item Low Typical High Source
Volume conversion 27 27 27 Standard U.S. volume conversion
Checked 2026-05-10 · high confidence
80 lb bag yield 0.55 0.6 0.62 QUIKRETE bag-yield reference
Checked 2026-05-10 · medium confidence
Ready-mix price 119 145 175 HomeGuide concrete price and Homewyse slab benchmarks
Checked 2026-05-10 · low confidence

Last reviewed: May 9, 2026. These values are planning defaults, not live prices.

Common mistakes

  • Measuring thickness in inches but forgetting to convert to feet.
  • Ignoring gravel base, forms, reinforcement, and finishing tools.
  • Trying to use bags for a slab that is better handled by ready-mix delivery.

FAQ

When should you use ready-mix?

Large slabs are usually better as ready-mix because bag mixing becomes slow and inconsistent.

Does this include reinforcement?

Only as a broad shopping-list reminder. Rebar or mesh needs depend on slab use and local practice.

Is this structural advice?

No. It is an early volume and cost estimate.

Limitations

This calculator does not replace local code, engineering, or site-specific slab design. Sub-base, drainage, reinforcement, and access matter.

This estimate is for planning only. It is not a contractor quote, engineering advice, or permit review.

Next step

Measure once more, compare the result with a real quote or shopping cart, and review the assumptions before buying materials.

Read the DIY vs contractor guide for this project

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