Post Hole Concrete Calculator
Calculate how many bags of concrete to buy for fence posts, deck posts, and mailbox posts. Get bags per hole and total weight estimate.
Last updated: April 12, 2026
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Worked Examples
A standard 6-foot fence with 10 posts needs about 10 bags of 80lb concrete. Add 1-2 extra bags for spillage.
Deck posts need deeper holes and larger diameter. Consider store delivery for orders over 500 lbs.
Post Hole Sizing: Rule of Thumb
Two simple rules for sizing your post holes correctly. Following these ensures your posts have enough concrete support and won't shift over time.
For a 4×4 post (3.5" actual), use an 8" to 10" diameter hole. This gives about 2" of concrete around the post for proper support.
A 6-foot fence needs at least a 24" deep hole. In cold climates, dig below the frost line to prevent winter heaving.
Concrete settles and some spills during pouring. Buy 1-2 extra bags to avoid running short mid-project.