Concrete Bag Calculator
Count 40, 60, or 80 lb concrete mix bags from slab length, width, and thickness. See cubic yards too if a ready-mix truck is cheaper.
How to use this concrete bag calculator
A concrete bag calculator answers the home-center question: how many sacks of mix, not how many truck yards. Each 80 lb bag yields about 0.60 cubic feet; 60 lb about 0.45; 40 lb about 0.30. Once you pass roughly a cubic yard (about 45 bags of 80 lb), a ready-mix truck is cheaper and far less miserable.
This page is bag-first. The Concrete Calculator and Concrete Slab Calculator lead with cubic yards for patio pours. Add 5–10% waste for uneven subgrade. Mix with the water on the bag — extra water weakens the slab.
Formula
Worked example
A 10×10 ft slab, 4 in thick, 10% waste is 36.67 cu ft. At 0.60 cu ft per 80 lb bag that is 62 bags.
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Frequently asked questions
How many 80 lb bags of concrete do I need?
Cubic feet ÷ 0.60, then round up. A 10×10×4″ slab with 10% waste is about 62 bags of 80 lb mix.
How many 60 lb bags in a cubic yard?
About 60 bags (27 ÷ 0.45).
Bags or a concrete truck?
Bags for piers, small pads, and fence posts. Call a truck above about 1 cubic yard.
Does bag size change volume?
Yes. 80 lb bags yield more than 60 or 40. Pick the sack you will actually carry.
Is this the same as the slab calculator?
The slab tool prices a truck first and lists bags in the details. This tool’s headline is the bag count.
Results are estimates for informational purposes and are not financial, legal, or professional advice. Last reviewed 2026-08-20.