Concrete Calculator
Calculate how much concrete you need in cubic yards, number of bags, and estimated cost. Enter length, width, and depth for slabs, footings, columns, or walls.
What Is a Concrete Calculator?
A concrete calculator estimates the volume of concrete needed for a construction project. It converts your length, width, and depth measurements into cubic yards — the standard unit for ordering ready-mix concrete. The calculator also converts to bag counts for smaller projects where bagged concrete is more practical.
Concrete is sold by the cubic yard for truck delivery and by the bag (60-lb or 80-lb) for hand-mixed projects. One cubic yard equals 27 cubic feet and covers approximately 81 square feet at 4 inches thick.
How the Concrete Calculator Works
Since depth is commonly measured in inches, the calculator converts inches to feet first by dividing by 12. The final volume in cubic feet is divided by 27 to get cubic yards.
Step-by-Step Instructions
Concrete Coverage Table
| Thickness | Area per Cubic Yard | 80-lb Bags per 10×10 |
|---|---|---|
| 2 inches | 162 sq ft | 23 bags |
| 3 inches | 108 sq ft | 34 bags |
| 4 inches | 81 sq ft | 45 bags |
| 5 inches | 64.8 sq ft | 56 bags |
| 6 inches | 54 sq ft | 67 bags |
| 8 inches | 40.5 sq ft | 90 bags |
| 12 inches | 27 sq ft | 134 bags |
Bags vs. Ready-Mix: When to Use Each
Use bagged concrete for projects under 1 cubic yard (approximately 45 bags of 80-lb mix). Bag mixing is practical for post holes, small pads, and repair work. Each 80-lb bag yields 0.60 cubic feet of concrete.
Use ready-mix delivery for projects over 1 cubic yard. Truck delivery is faster, produces more consistent concrete, and costs less per yard than bagged mix. Minimum delivery is typically 1 cubic yard with a short-load fee for orders under 5 yards.
Common Mistakes When Ordering Concrete
- Measuring depth in feet instead of inches. A 4-inch slab entered as 4 feet produces 12× too much concrete.
- Skipping the waste factor. Uneven subgrade, form irregularities, and spillage consume 10-15% of the total volume.
- Ordering exactly the calculated amount. Running short during a pour creates cold joints — a structural weakness. Order 10% extra.
- Ignoring minimum delivery. Ready-mix companies charge short-load fees ($50-$100) for orders under 5-10 yards.
- Not accounting for rebar chairs. Rebar and wire mesh displace concrete volume. This is already covered by the waste factor, but extremely heavy reinforcement may need 12-15% extra.
Pro Tip: Concrete weighs approximately 4,050 lbs per cubic yard (150 lbs per cubic foot). Ensure your subgrade and forms can support this weight during the pour.
Related Calculations
- Stud Calculator — Wall framing after foundation work
- Rafter Calculator — Roof framing calculations
- Gravel Calculator — Sub-base material for concrete slabs
- Drywall Calculator — Interior finishing after framing
- Fence Post Calculator — Post hole concrete requirements