Ready-mix or bagged concrete
Compare project size, bag yield, access, and delivery minimums.
Tools
Concrete Slab Calculator
Estimate concrete volume in cubic yards and bags for patios, shed bases, and small slabs.
Calculator
Estimate concrete slab volume
Calculate concrete volume for a slab, patio, shed base, or small DIY pad.
Concrete volume
1.48 cu yd
With waste
1.63 cu yd
Concrete volume
40.0 cu ft
80 lb bags
67 bags
Formula assumptions
- Slab area equals length x width.
- Thickness is converted from inches to feet.
- Cubic yards are cubic feet divided by 27.
- 80 lb bag estimate assumes about 0.6 cubic feet per bag.
Planning summary
Concrete slab estimate Slab size: 10 ft x 12 ft Thickness: 4 in Concrete: 1.48 cu yd With waste: 1.63 cu yd 80 lb bags: 67 Formula: length x width x thickness; waste is added to cubic yards.
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Estimates are for planning only. Check local prices, site conditions, product labels, and applicable rules before buying materials or building.
Explanation
How concrete slab volume is calculated
How the calculation works
The calculator multiplies length by width by slab thickness. Thickness is converted from inches to feet, cubic feet are divided by 27 for cubic yards, and a waste percentage can be added.
Example calculation
For a 10 by 12 foot slab at 4 inches thick, the estimate is 1.48 cubic yards. With 10% waste, plan about 1.63 cubic yards.
Pour planning
Plan the slab beyond cubic yards.
Concrete quantity is only the first number. Thickness, bags versus delivery, base prep, forms, tools, and curing all affect the finished slab.
Convert volume into concrete bags
Small slabs and pads may be easier with bagged concrete, but bag yield matters.
Read guidePrepare for pour day
Forms, gravel base, reinforcement, tools, finishing, and curing need a plan before concrete arrives.
Read guideChoose slab thickness
Thickness affects volume, cost, strength, base prep, and project suitability.
Read guideCompare common slab sizes
Use size examples to understand how footprint and thickness move the budget.
Read guideMaterials checklist
Concrete slab shopping checklist
Concrete volume is only one part of a slab. Forms, base prep, tools, finishing, and curing supplies should be planned early.
BuildMetric may add affiliate links here later. Recommendations should stay practical, clearly disclosed, and tied to the project estimate.Read the affiliate disclosure.
Gravel base
A compacted base helps support the slab and manage drainage.
Form boards and stakes
Forms control slab size, height, and finished edges.
Reinforcement
Wire mesh, rebar, or fiber may be needed depending on the slab.
Finishing and curing supplies
Plan screed, float, edger, broom, gloves, boots, and curing method.
Before buying
- Confirm slab thickness before ordering.
- Add waste for uneven base, forms, and spillage.
- Check local requirements for structural or vehicle-supporting slabs.
FAQ
Concrete slab calculator questions
How do I calculate concrete for a slab?
Multiply slab length by width by thickness. Convert thickness from inches to feet, then divide cubic feet by 27 for cubic yards.
Should I add waste to a concrete order?
Yes. Many small projects add about 5% to 10% so the pour does not come up short.
How much does an 80 lb bag of concrete make?
A common planning estimate is about 0.6 cubic feet per 80 lb bag.
Can this replace a contractor estimate?
No. It is for early planning only. Slabs may need base prep, reinforcement, forms, permits, and local code checks.
Formula and assumptions
How this estimate should be used
Estimating concrete for patios, shed slabs, utility pads, and small homeowner concrete projects.
Formula summary
- Slab volume = length x width x thickness
- Thickness is converted from inches to feet before calculating cubic feet
- Cubic yards = cubic feet / 27
- Final estimate can include a selected waste allowance
Planning assumptions
- The calculator estimates concrete volume only, not structural design.
- Base preparation, forms, reinforcement, drainage, and local code may affect the project.
- Small pours often need a 5% to 10% buffer to avoid running short.
Next steps
Turn the estimate into a plan.
Use the result as a starting point, then check the supporting guide or continue with the next calculator before buying materials.
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