Concrete Calculator: How Many Bags Do You Need?
Calculate exactly how much concrete you need for your project. Covers slabs, footings, columns, and post holes.
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You're pouring a patio and you need to know how many 80-pound bags to buy. Too few and you make a second trip. Too many and you've got bags of concrete hardening in your garage. Here's the math.
Quick Formula
Length (ft) x Width (ft) x Depth (ft) = Cubic feet
Cubic feet / 27 = Cubic yards
For bags: One 80-lb bag covers 0.6 cubic feet. One 60-lb bag covers 0.45 cubic feet.
Use the Calculator
The Concrete Calculator handles slabs, footings, columns, and post holes. Enter your dimensions and get exact bag counts for both 60-lb and 80-lb bags. It even adds 10% for waste.
Common Projects
4x4 fence post hole (10" diameter, 24" deep): About 1 bag per hole.
10x10 patio slab (4" thick): About 56 bags (80-lb).
Sidewalk (3ft wide, 20ft long, 4" thick): About 34 bags (80-lb).
Tips
Always buy 10% more than calculated. You'll lose some to spillage, uneven ground, and mixing waste. Returning unopened bags is easy. Making a second trip to the store with wet concrete drying is not.
For anything over 1 cubic yard (roughly 45 bags), consider ordering a ready-mix concrete truck. It's cheaper per yard and way less labor than mixing 45 individual bags.