Post Hole Concrete Bag Calculator
Find out how many bags of concrete it takes to set posts. Enter the hole diameter and depth, the post width, the number of posts, and the yield of one bag.
How to figure concrete bags per post
- Enter the hole diameter and depth in inches.
- Enter the square post width and how many posts you are setting.
- Set the cubic feet one bag yields, then read off the bags to buy.
Examples
10 in hole, 30 in deep, 4 in post, 60 lb bags
Hole 10 in by 30 in, post 4 in, 1 post, bag yields 0.45 cu ft
1.086 cu ft per hole, 3 bags
Frequently asked questions
How much concrete do I need for one post?
Take the volume of the round hole, a cylinder of the diameter and depth, and subtract the volume of the post. The remainder is the concrete per hole, which this calculator converts to bags.
How deep and wide should a post hole be?
A common guide is a hole three times the post width and about a third of the post height deep, below the frost line. Wider, deeper holes use more concrete, so set the dimensions to match your plan.
How many cubic feet does a bag of concrete yield?
A 60 pound bag yields about 0.45 cubic feet and an 80 pound bag about 0.6 cubic feet. Check the bag, since fast-setting and high-strength mixes can differ, and enter that yield here.
Should I round bags up?
Yes. Concrete is sold in whole bags, so the count is always rounded up. Having one spare bag on site avoids a stop mid-pour, and it lets you top off a hole that turned out a little wider.
Does the post size really change the bag count?
Yes, a thicker post displaces more concrete and lowers the amount the hole needs. A 4 by 4 takes a bit more than a 6 by 6 in the same hole, since the larger post leaves less space to fill.
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