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Choose units
Select feet and inches or metric measurements.
Free Construction Calculator
Concrete Calculator – Yards, Bags & Cost
Calculate how much concrete you need for a slab, pad or footing. Get estimates in cubic yards, cubic feet and cubic meters, plus concrete bag quantities, waste allowance and approximate material cost.
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Concrete Project Details
Enter the dimensions of your concrete project. Results update automatically.
Use this option for patios, floors, sidewalks and rectangular concrete slabs.
The price field is optional. Use a local ready-mix supplier price for a more useful cost estimate.
How much concrete do I need?
Multiply the length by the width and thickness to find concrete volume. In U.S. measurements, convert thickness from inches to feet first, then divide cubic feet by 27 to get cubic yards. Adding about 5% to 10% extra can help cover uneven excavation, spills and small measurement differences.
How to Use the Concrete Calculator
2
Enter dimensions
Enter the project length, width and thickness or footing depth.
3
Add waste
Use a waste allowance to cover normal job-site variation.
4
Review results
See cubic yards, cubic meters, bag quantities and estimated cost.
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Concrete Volume Formula
For a rectangular slab, pad or footing, concrete volume is calculated by multiplying length, width and thickness.
Length × Width × Thickness = Volume
When using feet and inches, divide the thickness in inches by 12 before multiplying. Then divide the total cubic feet by 27 to convert cubic feet to cubic yards.
Example: 10 ft × 10 ft Concrete Slab
For a 10 ft long × 10 ft wide slab that is 4 inches thick:
4 inches ÷ 12 = 0.333 ft
10 × 10 × 0.333 = 33.3 cubic feet
33.3 ÷ 27 = 1.23 cubic yards
With 10% extra = approximately 1.36 cubic yards
Concrete Bag Yield Guide
Premixed concrete bag yields vary slightly by manufacturer. These approximate values are useful for estimating small projects.
| Bag Size | Approx. Yield | Approx. Bags per Cubic Yard |
|---|---|---|
| 40 lb | 0.30 ft³ | 90 bags |
| 60 lb | 0.45 ft³ | 60 bags |
| 80 lb | 0.60 ft³ | 45 bags |
Always verify the yield on the specific product bag before buying material.
How Much Extra Concrete Should You Order?
Ordering exactly the calculated volume can leave you short if the excavation is slightly deeper, forms are uneven or material is spilled during placement.
Simple, well-measured projectAbout 5%
Typical slab or footingAbout 10%
Irregular excavationConsider more
Common Concrete Slab Thicknesses
Required thickness depends on the project, soil, reinforcement, loads and local building requirements. The values below are only general planning examples.
Walkway or small patioOften around 4 in
Residential slabOften around 4 in
Heavier vehicle areasMay require 5–6+ in
Structural projects should follow local code and engineering requirements.
Concrete Calculator FAQ
How many cubic feet are in one cubic yard of concrete?+
One cubic yard contains 27 cubic feet. Divide cubic feet by 27 to convert a concrete volume to cubic yards.
How many 80 lb bags of concrete make a cubic yard?+
Using an approximate yield of 0.60 cubic feet per 80 lb bag, about 45 bags are needed for one cubic yard. Actual product yields may differ.
How many 60 lb bags make a cubic yard?+
At an approximate yield of 0.45 cubic feet per bag, about 60 bags are needed for one cubic yard.
Should I add extra concrete to my estimate?+
Many projects include about 5% to 10% extra concrete for uneven excavation, spills and small measurement differences.
How do I calculate concrete for a slab?+
Multiply slab length by width and thickness. If your thickness is measured in inches, convert it to feet before calculating cubic feet, then divide by 27 for cubic yards.
Is ready-mix concrete better than bags for a large project?+
For larger pours, ready-mix delivery can be more practical than mixing a large number of bags. Small repairs and small pads are often suitable for bagged concrete.
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Planning Disclaimer
This calculator provides estimates for planning and budgeting. Actual concrete requirements can vary because of excavation accuracy, soil conditions, form dimensions, compaction, waste, supplier specifications and construction requirements. Verify quantities with your concrete supplier or construction professional before ordering material.