Concrete Calculator
Calculate concrete for your project
Multiple shapes
Cubic yards and bags
Tips included
You're pouring a patio slabβ10 feet by 12 feet, 4 inches thick. How many bags of concrete do you need? Or should you order a truck? Will 80-pound bags be enough, or will you need a hundred of them?
Concrete quantity calculation prevents two disasters: running out mid-pour (disastrous for structural integrity) and ordering way too much (expensive and wasteful). This calculator tells you exactly what you need.
What is Concrete Calculation?
Concrete calculation determines the volume of concrete needed for a project, typically measured in cubic yards (for ready-mix) or bags (for bagged concrete). Volume depends on dimensions: length Γ width Γ depth.
The formulas:
Volume (cubic feet) = Length Γ Width Γ Depth (all in feet)
Volume (cubic yards) = Cubic feet Γ· 27
For depth in inches: divide by 12 first
Typical coverage per 80lb bag: 0.6 cubic feet
Bags needed = Volume (cu ft) / 0.6
Concrete doesn't pour perfectly. Uneven subgrade, spillage, and form bulging consume material. Always order 10% extra.
Why People Actually Need This Tool
Once mixed, concrete has a limited working time. Running out mid-pour means a cold jointβa weak point in your structure.
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Patio slabs β Calculate material for outdoor living spaces.
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Driveways β Estimate concrete for vehicle surfaces.
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Footings β Size foundation concrete requirements.
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Posts β Determine concrete for fence/deck posts.
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Sidewalks β Calculate path and walkway needs.
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Steps β Estimate material for stair construction.
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Cost estimation β Budget accurately for materials.
How to Use the Concrete Calculator
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Enter dimensions β Length, width, depth (in feet or inches).
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Select project type β Slab, footing, column, stairs, etc.
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View results β Cubic yards for trucks, bags for manual mixing.
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Add waste factor β Include 10% extra for safety margin.
| Project Type | Typical Depth | Coverage Notes |
|---|---|---|
| Patio slab | 4 inches | Standard residential thickness |
| Driveway | 4-6 inches | 6" for heavier vehicles |
| Sidewalk | 4 inches | Standard path thickness |
| Footings | 8-12 inches | Below frost line, per code |
| Post holes | Varies | 1/3 of post length in ground |
| Garage floor | 4-6 inches | 6" with heavy equipment |
Under 1 cubic yard: bags are practical. 1-3 yards: borderline. Over 3 yards: ready-mix truck is more economical and consistent.
Real-World Use Cases
1. The Patio Pour
Context: 12' Γ 16' patio slab, 4 inches thick.
Problem: How much concrete needed?
Solution: 12 Γ 16 Γ (4/12) = 64 cu ft = 2.37 cu yards. Order 2.5 yards + 10% = ~2.75 yards.
Outcome: Enough concrete to complete pour without running short.
2. The Fence Posts
Context: 20 fence posts, each hole 10" diameter Γ 24" deep.
Problem: Total concrete for all posts?
Solution: Each hole: Ο Γ (5")Β² Γ 24" = 1,885 cu in = 1.09 cu ft. Total: 20 Γ 1.09 = 21.8 cu ft.
Outcome: ~37 80-lb bags needed (covering ~0.6 cu ft each).
3. The Driveway Extension
Context: Adding 10' Γ 20' concrete pad to existing driveway.
Problem: Concrete quantity at 5" thickness?
Solution: 10 Γ 20 Γ (5/12) = 83.3 cu ft = 3.1 cu yards + 10% = 3.4 yards.
Outcome: Order 3.5 yards from ready-mix truck.
4. The Footing Calculation
Context: Foundation footing 8" wide Γ 16" deep Γ 60 linear feet.
Problem: Volume for continuous footing?
Solution: (8/12) Γ (16/12) Γ 60 = 53.3 cu ft = 2 cu yards.
Outcome: Accurate footing material estimate for foundation.
5. The Step Repair
Context: Replacing 3 concrete steps. Each: 36" wide Γ 12" deep Γ 7" rise.
Problem: Total concrete for three steps?
Solution: Each step: (36/12) Γ (12/12) Γ (7/12) = 1.75 cu ft. Three steps: ~5.25 cu ft.
Outcome: ~9 bags of 80-lb concrete for step repair.
6. The Column Pour
Context: Four deck pier columns, each 12" diameter Γ 36" tall.
Problem: Concrete for all columns?
Solution: Each: Ο Γ (6")Β² Γ 36" = 4,072 cu in = 2.36 cu ft. Four columns: 9.44 cu ft.
Outcome: ~16 bags with waste allowance.
7. The Cost Comparison
Context: Project needs 2.5 cubic yards. Should I bag it or truck it?
Problem: Which is more economical?
Solution: 2.5 yards Γ· 0.6 Γ 27 = ~113 bags at $6 = $678. Truck at $150/yard = $375.
Outcome: Ready-mix truck saves $300 and hours of mixing.
Common Mistakes and How to Avoid Them
A 4-foot thick slab is very different from a 4-inch thick slab. One is a bunker, one is a patio. Check your units.
Privacy and Data Handling
This Concrete Calculator operates entirely in your browser.
- No calculations are sent to any server.
- No project data is stored.
- No account required.
- Works completely offline.
Your construction plans stay private.
Conclusion
Accurate concrete calculation saves money and prevents failed pours. Too little means structural weakness. Too much means wasted material and disposal hassles.
This calculator handles the math for any shape: slabs, footings, columns, or custom dimensions. Enter measurements, get quantities, order with confidence.
Pour it right the first time.