Concrete Bag Calculator
Estimate how many ready-mix bags of concrete (40 lb, 50 lb, 60 lb, or 80 lb) you need for a given project volume and weight requirements.
Calculation Results
Estimated count of dry pre-mix concrete bags required to fill the volume.
The combined total weight of dry mix bags to transport or purchase.
How This Calculator Works
To calculate bags of concrete mix needed:
- Enter the total volume of concrete required for the project (you can enter it in cubic feet, cubic yards, or cubic meters).
- Select the concrete bag weight you plan to buy (80 lb is standard for structural tasks).
- Add a waste buffer margin (10% is standard for uneven ground excavation).
- The calculator outputs the number of individual bags and the total dry weight.
Formula & Calculations
The number of ready-mix concrete bags is calculated using standard volumetric yields for each bag weight:
- 80 lb bag: Yields
0.60cubic feet of wet concrete. - 60 lb bag: Yields
0.45cubic feet of wet concrete. - 50 lb bag: Yields
0.375cubic feet of wet concrete. - 40 lb bag: Yields
0.30cubic feet of wet concrete.
Mathematically, the concrete bag yield is exactly proportional to weight: Yield = Weight × 0.0075 cubic feet.
The bag count is calculated as: Bags = ceil((Volume × (1 + Waste / 100)) / Yield).
Step-by-Step Calculation Examples
Small Post Set or Slab (10 cu ft volume)
Estimating how many 80 lb bags are needed to fill 10 cubic feet with a 10% waste buffer.
- volume: 10
- bag_size: 80
- waste: 10
- bags_needed: 19
- total_weight: 1520.0 lb
Frequently Asked Questions
How many 80 lb bags of concrete does it take to make a cubic yard?
It takes exactly 45 bags of 80 lb concrete mix to equal one cubic yard (27 cubic feet). Each 80 lb bag yields 0.60 cubic feet.
How many 60 lb bags of concrete are in a cubic yard?
It takes exactly 60 bags of 60 lb concrete mix to yield one cubic yard of wet concrete. Each 60 lb bag yields 0.45 cubic feet.
Which concrete bag size is best for post holes?
For small post holes, 50 lb or 60 lb bags are easier to lift and mix by hand. For larger structural footings, 80 lb bags are the industry standard and offer the best volume-to-price ratio.
Do I need to add gravel or sand to bag concrete?
No. Ready-mix concrete bags (like Quikrete or Sakrete) already contain Portland cement, sand, and gravel blended in the correct proportions. You only need to add water.
How much water do I add to an 80 lb bag of concrete?
Typically, a standard 80 lb bag of concrete mix requires about 3 quarts (2.8 liters) of clean water. Be careful not to add too much water, as it weakens the cured concrete strength.