Bagged Concrete Calculator
Adjust the parameters below to compute materials and estimate project costs.
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Calculation Formulas & Steps
Bags needed = Total Volume (cu ft) ÷ Bag Yield (cu ft). Include a 10% waste buffer and round up.
Worked Example (Step-by-Step Math)
Yield depends on weight.
80lb bag yields 0.60 cubic feet.Divide needed volume by bag yield.
15 cu ft ÷ 0.60 = 25 bagsAdd 10% and round to next whole bag.
25 × 1.10 = 27.5 ≈ 28 bagsConcrete Bag Yield Reference
Wet volume yields of concrete mixes.
| Project Condition | Reference Metric |
|---|---|
| 80 lb Bag | 0.60 cubic feet |
| 60 lb Bag | 0.45 cubic feet |
| 50 lb Bag | 0.37 cubic feet |
| 40 lb Bag | 0.30 cubic feet |
Critical Mistakes to Avoid
- !Mistake 1: Mixing a few bags at a time without keeping the pour wet, creating "cold joints" where sections fail to bond.
- !Mistake 2: Underestimating water volume, leading to dry pockets inside the concrete.
Frequently Asked Questions
How many 80 lb bags of concrete make up a cubic yard?
There are exactly forty-five (45) bags of 80 lb concrete in one (1) cubic yard. Since a cubic yard is 27 cubic feet and one 80 lb bag yields 0.60 cubic feet of wet concrete: 27 ÷ 0.60 = 45 bags. If you are calculating with a 10% waste allowance, purchase 50 bags.
How do I calculate the number of concrete bags needed for a post hole?
To calculate concrete bags for a post hole, find the volume of the cylindrical hole (π × r² × depth) and subtract the volume of the post inside the hole. For a standard 10" wide hole, 36" deep containing a 4x4 post, you will need approximately 1.4 cubic feet of concrete, which is 2.5 bags of 80 lb mix. Round up to 3 bags per hole.
How much does a cubic yard of bagged concrete cost?
Since one cubic yard requires 45 bags of 80 lb concrete, at an average cost of $6.50 to $8.00 per bag, a yard of bagged concrete costs $290 to $360 for materials alone. This is about double the cost of bulk ready-mix per yard, but avoids ready-mix short-load delivery fees.
Can I mix bagged concrete directly in the post hole?
Yes, using the "dry pour" method for fence posts. Dump the dry concrete mix into the hole, pour in the recommended water, and stir/pierce with a rod to ensure water saturates the bottom. However, for structural decks or load-bearing footings, always mix with water before pouring.
How many 60 lb bags of concrete are in a cubic yard?
It takes exactly sixty (60) bags of 60 lb concrete to make one (1) cubic yard. Each 60 lb bag yields 0.45 cubic feet of wet concrete: 27 ÷ 0.45 = 60 bags.
How much water goes into an 80 lb bag of concrete?
Typically 3 to 4 quarts of clean water. Add water gradually until you reach an oatmeal consistency.
What happens if I add too much water to bagged concrete?
Adding excess water makes the mix easier to pour but severely dilutes the cement paste, reducing structural strength and causing cracks.
Complete Tools Checklist
- Mixing Tub or Wheelbarrow
- Hoe or Shovel
- Water Hose / Bucket
- Trowel