# Concrete bag calculator

This bag concrete estimator turns the size of your slab, cement pad or post holes into cubic yards and the number of 40–90 lb bags you need, including a waste allowance.

## How the calculation works

Bags = volume ÷ bag yield × (1 + waste %), rounded up. Slab volume (cu ft) = length (ft) × width (ft) × thickness (in) ÷ 12. A post hole holds (0.7854 × diameter² − post area) × depth ÷ 1,728 cu ft when measured in inches. One cubic yard is 27 cu ft.

Typical yields are about 0.30 cu ft for a 40 lb bag, 0.45 for 60 lb, 0.60 for 80 lb and 0.675 for 90 lb. Yields vary by mix and plant, so always confirm the figure printed on your bag.

## FAQ

### How many 80 lb bags of concrete are in a yard?

About 45. A cubic yard is 27 cu ft and an 80 lb bag yields roughly 0.60 cu ft, so 27 ÷ 0.60 = 45 bags before waste.

### How many bags of concrete do I need for a fence post?

A 4×4 post in a 10 in wide, 30 in deep hole needs about 1.15 cu ft of concrete — two 80 lb bags or three 60 lb bags before waste (the calculator adds your waste allowance on top).

### How many 60 lb bags of concrete make a cubic yard?

About 60 bags, because each 60 lb bag yields roughly 0.45 cu ft and a cubic yard is 27 cu ft.

### How do you calculate concrete yardage?

Measure length × width in feet and multiply by thickness in inches ÷ 12 to get cubic feet, then divide by 27 to get cubic yards. A 10 × 10 ft pad 4 in thick is 33.3 cu ft, or 1.23 cubic yards.

### Does Evergreen Packaging sell concrete?

No. We manufacture the bags — PP woven and paper valve bags for cement, concrete and mortar plants. See our cement bag guide.