Concrete Volume Calculator
Enter the dimensions of your concrete project below to instantly calculate how many cubic yards and bags of concrete you need. Includes a configurable waste factor for real-world accuracy.
What is Concrete Volume?
Concrete volume is the total amount of concrete required to fill a three-dimensional space, such as a slab, footing, or column. Knowing the exact volume prevents both costly over-ordering and project-delaying shortages. Concrete is sold by the cubic yard (ready-mix trucks) or in bags for smaller projects. One cubic yard equals 27 cubic feet and covers approximately 81 square feet at 4 inches thick.
How to Calculate
- Measure the length of your project area in feet
- Measure the width in feet
- Determine the depth (thickness) in inches
- Add a waste factor (10% is standard for most projects)
- The calculator will show cubic yards, cubic feet, and bag counts
Formula
The basic formula is: Volume (cubic feet) = Length (ft) x Width (ft) x Depth (in) / 12. To convert to cubic yards, divide cubic feet by 27. The waste factor accounts for spillage, uneven subgrade, and slight over-excavation. Industry standard is 10% for slabs and 15% for footings and irregular shapes.
Example Calculation
For a 10 ft x 12 ft patio slab that is 4 inches thick with 10% waste: Volume = 10 x 12 x (4/12) = 40 cubic feet. With 10% waste = 44 cubic feet = 1.63 cubic yards. You would need approximately 74 bags of 80 lb concrete, or you could order 2 cubic yards of ready-mix for a project this size (minimum delivery is typically 1 yard).
Frequently Asked Questions
How much does a cubic yard of concrete weigh?
A cubic yard of standard concrete weighs approximately 4,050 pounds (1,837 kg). This is important to know for structural load calculations and when estimating delivery truck capacity.
Should I order extra concrete beyond the waste factor?
The 10% waste factor built into this calculator covers most situations. However, for irregular shapes, slopes, or projects with many forms, consider increasing to 15%. Ready-mix trucks typically deliver in 0.25-yard increments, so round up to the nearest quarter yard.
How many 80 lb bags of concrete are in a cubic yard?
You need approximately 45 bags of 80 lb concrete mix to make one cubic yard. Each 80 lb bag yields roughly 0.6 cubic feet of mixed concrete.
When should I use bags vs. ready-mix delivery?
Use bags for projects under 1 cubic yard (small footings, post holes, repairs). For anything over 1 cubic yard, ready-mix delivery is more cost-effective and produces more consistent results. The crossover point is typically around 0.75-1 cubic yard.
What depth should I pour my concrete slab?
Standard residential slabs (patios, walkways) are 4 inches thick. Driveways and garage floors should be 5-6 inches. Load-bearing slabs or areas with vehicle traffic need 6-8 inches minimum. Always check local building codes.
How long does concrete take to cure?
Concrete reaches approximately 70% of its full strength in 7 days and 99% in 28 days. You can walk on it after 24-48 hours, drive on it after 7 days, and place heavy loads after 28 days. Keep it moist during the first 7 days for optimal curing.