Concrete Calculator
A concrete calculator computes the required volume of ready-mix concrete in cubic yards and standard commercial bags for slabs, footings, and post holes. Using the formula Volume = Length × Width × Depth, it confirms that a 10-by-10-foot patio slab poured 4 inches thick requires 1.23 cubic yards.
By Sofia Marchetti (Home & Wellness Reviewer) · Reviewed by Daniel OkoroUpdated · Published
Length (ft)
0ft
Width (ft)
0ft
Thick (in)
0in
CONCRETE VOLUME
Total: 0.0 cu ft | Approx. 0 bags (80 lb)
How Does the Concrete Calculator Work?
- Enter slab length, width, and thickness in inches (4 inches standard for patios/walkways).
- For round footings: enter hole diameter and depth.
- Outputs total cubic yards and corresponding bag counts for 60lb and 80lb sacks.
What Is the Concrete Formula?
Cubic Yards = (Length ft × Width ft × Thickness in / 12) / 27
Volume in cubic feet divided by 27 (27 cubic feet = 1 cubic yard).
Variables
Cubic Yards:Volume measure for ready-mix trucks
80lb Bag:Yields approx. 0.60 cubic feet (45 bags / yd³)
How Do You Calculate Concrete Step by Step?
A 10×12 ft patio slab poured at 4 inches thicknessLength: 12 ft
Width: 10 ft
Thickness: 4 in
Volume: 12 × 10 × (4 / 12) = 40 cubic feet
Cubic yards: 40 ÷ 27 = 1.48 cubic yards
80 lb bags needed: 40 ÷ 0.60 = 67 bags (approx 67 bags)
Final Solution:1.48 Cubic Yards (or 67 eighty-pound bags)
Ready-mix bags per cubic yard (approximate yield)
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 80 lb bag | 0.60 cu ft | 45 bags |
| 60 lb bag | 0.45 cu ft | 60 bags |
| 40 lb bag | 0.30 cu ft | 90 bags |
Concrete Questions and Answers
It takes 45 bags of 80 lb concrete (or 60 bags of 60 lb concrete) to make 1 cubic yard.