Concrete Bag Calculator
Wondering how many bags of concrete do I need? This concrete bag calculator turns your project size into a bag count for 40, 60, and 80 lb premixed bags. Enter the dimensions, pick a waste allowance, and it tells you how many bags to buy — plus the equivalent in cubic yards if ready-mix makes more sense.
How to use this calculator
- Enter the length, width, and thickness of your pour.
- Add a waste allowance — bags are sold whole, so a little extra avoids a second trip.
- Compare the 40, 60, and 80 lb bag counts in the results.
- If the count climbs above 40–50 bags, check the cubic-yard figure — ready-mix is usually easier.
The formula
First find the volume in cubic feet, then divide by the yield of one bag. The standard yields are 0.60 ft³ for an 80 lb bag, 0.45 ft³ for a 60 lb bag, and 0.30 ft³ for a 40 lb bag. Always round up to whole bags:
Bags = Volume (ft³) ÷ Bag yield (ft³), rounded up
Worked example. A 6 ft × 4 ft pad at 4 inches thick is 6 × 4 × 0.333 = 8 cubic feet. Divide by 0.60 and you need 14 × 80 lb bags, or by 0.45 for 18 × 60 lb bags, or by 0.30 for 27 × 40 lb bags.
Frequently asked questions
How many bags of concrete do I need?
Work out your volume in cubic feet, then divide by the bag yield: an 80 lb bag makes about 0.60 ft³, a 60 lb bag about 0.45 ft³, and a 40 lb bag about 0.30 ft³. Always round up to whole bags.
How many 80 lb bags of concrete make a yard?
About 45 bags. One cubic yard is 27 cubic feet, and each 80 lb bag yields roughly 0.60 ft³, so 27 ÷ 0.60 ≈ 45 bags.
How many 60 lb bags are in a yard?
Around 60 bags, since a 60 lb bag yields about 0.45 ft³ and 27 ÷ 0.45 = 60.
How many 40 lb bags are in a yard?
About 90 bags. A 40 lb bag yields roughly 0.30 ft³, and 27 ÷ 0.30 = 90.
When is bagged concrete cheaper than ready-mix?
Bags win for small jobs up to about half a cubic yard. Past that, mixing dozens of bags by hand becomes slow and ready-mix delivery is usually cheaper and more consistent.