Concrete slab calculator
Estimate concrete volume for slabs, post holes, footings, sonotubes, known volume, 40/60/80 lb bags, ready-mix cost, and labor range.
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Concrete slab calculator
May 9, 2026
12 ft by 10 ft slab at 4 in thick.
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
- 0.60 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.
Calculator setup
12 ft by 10 ft slab at 4 in thick.
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
- 0.60 cu ft per 80 lb bag
- 10% waste buffer
- U.S. near average; pricing data: U.S. near average pricing
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What this calculator estimates
This concrete calculator starts from the measurements and options you enter, then estimates material quantity, waste, cost ranges, labor ranges, and a starter shopping list.
Results adapt to the selected region and unit settings, so the estimate is not locked to one market or measurement system.
Report confusing results, missing options, or assumptions that look off.
How this is calculated
- Project type chooses slab rectangle, cylindrical post holes or tubes, continuous footing, or known volume.
- Slab cubic feet are length x width x thickness in feet.
- Post holes and sonotubes use cylinder volume from diameter, depth, and count.
- Footings use length x width x depth.
- Cubic yards divide cubic feet by 27 and round up to the nearest tenth.
- Bag count uses the selected 40, 60, or 80 lb bag yield.
Assumption register
| Item | Low | Typical | High | Source |
|---|---|---|---|---|
| Volume conversion | 27 | 27 | 27 | Standard U.S. volume conversion Checked 2026-06-21 · high confidence |
| 80 lb bag yield | 0.55 | 0.6 | 0.62 | QUIKRETE bag-yield reference Checked 2026-06-21 · medium confidence |
| Ready-mix price | 130 | 155 | 185 | Concrete Network ready-mix price guide Checked 2026-06-21 · 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.
- Using an 80 lb bag count after deciding to buy 40 or 60 lb bags.
- Ignoring gravel base, forms, reinforcement, bracing, and finishing tools.
- Trying to hand-mix a slab or large footing 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.
Which project type should you choose?
Use slab for pads, post holes for fence or mailbox holes, footing for continuous trenches, sonotube for round piers, and custom volume when you already know the cubic footage.
Why does bag size matter?
A smaller bag covers less volume, so switching from 80 lb bags to 60 or 40 lb bags increases the bag count.
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.
Can this concrete calculator estimate cost by region?
Yes. The calculator uses the selected region and unit settings to adapt quantities, cost ranges, labor ranges, and assumptions.
How should you use the result before buying materials?
Use the result as a planning estimate, then compare it with a current supplier cart, contractor quote, or local project conditions before committing.
Limitations
This calculator estimates concrete quantity and broad planning cost. It does not replace local code, engineering, frost-depth guidance, load design, or site-specific slab, footing, or pier design.
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 how much concrete for fence posts guide
Read the how much concrete do I need guide
Read the how many concrete bags do I need guide
Read the how much concrete for a 10x10 slab guide
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