Concrete Bag Calculator Formula
Understand the math behind the concrete bag calculator. Each variable explained with a worked example.
Formulas Used
Total Volume
cubic_feet = volume_cuftTotal Volume
cubic_yards = volume_cuft / 27Bags Needed
bags_needed = ceil(volume_cuft / coverage_per_bag)Variables
| Variable | Description | Default |
|---|---|---|
length | Length(feet) | 10 |
width | Width(feet) | 10 |
depth | Depth / Thickness(inches) | 4 |
bag_size | Bag Size | 80 |
depth_ft | Derived value= depth / 12 | calculated |
volume_cuft | Derived value= length * width * depth_ft | calculated |
coverage_per_bag | Derived value= bag_size == 80 ? 0.6 : (bag_size == 60 ? 0.45 : 0.3) | calculated |
How It Works
How to Calculate Concrete Bags Needed
Formula
Bags = Total Cubic Feet / Coverage per Bag
| Bag Size | Yield (cu ft) | |----------|---------------| | 80 lb | 0.60 cu ft | | 60 lb | 0.45 cu ft | | 40 lb | 0.30 cu ft |
For small projects under 1 cubic yard, bagged concrete is more practical. For larger projects, order ready-mix from a concrete plant.
Worked Example
A 10 ft by 10 ft slab, 4 inches thick, using 80 lb bags.
length = 10width = 10depth = 4bag_size = 80
- 01Depth in feet: 4 / 12 = 0.333 ft
- 02Volume = 10 × 10 × 0.333 = 33.33 cu ft
- 03Cubic yards = 33.33 / 27 = 1.23 cu yd
- 04Bags (80 lb) = 33.33 / 0.60 = 55.6 → 56 bags
Ready to run the numbers?
Open Concrete Bag Calculator