Calculate exactly how many posts and bags of concrete you need. Enter your fence length and dimensions — get instant results.
Total length of your fence line
How deep posts are set in concrete (24-30" typical)
100 linear feet of fence
Concrete bags only. Does not include posts, labor, or other materials.
💡 Pro Tip: Buy 10% extra concrete to account for spillage and uneven holes. Fast-setting concrete lets you continue same-day.
* Estimates assume cylindrical holes with diameter 3x post width. Actual needs may vary based on soil conditions and hole shape.
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Our calculator uses industry-standard formulas and real concrete bag specifications.
Divides your fence length by spacing, then adds 1 for the end post. Formula: (length ÷ spacing) + 1.
Calculates cylindrical hole volume (π × r² × depth), minus the post volume, to get concrete needed.
Each bag size has a known yield: 40lb = 0.30 cu ft, 50lb = 0.375 cu ft, 80lb = 0.60 cu ft.
For a standard 4x4 wood fence post set 24 inches deep in a 12-inch diameter hole, you'll typically need 1-2 bags of 80lb concrete, 2-3 bags of 50lb concrete, or 3-4 bags of 40lb concrete. The exact amount depends on your hole diameter (usually 3x the post width) and depth.
Standard post spacing is 6-8 feet for most residential fences. Wood privacy fences typically use 6-foot spacing for better stability, while chain link fences can use 8-10 foot spacing. Never exceed 8 feet for wood fences, as panels may sag or become unstable.
The general rule is to bury 1/3 of the total post length. For a 6-foot fence, posts should be 8 feet long with 24-30 inches buried. At minimum, posts should be set 24 inches deep, or below the frost line in cold climates to prevent heaving.
The hole diameter should be 3 times the width of your post. For a standard 4x4 post (3.5 inches actual), dig a 10-12 inch diameter hole. For 6x6 posts, use a 16-18 inch hole. This provides enough space for proper concrete coverage around the post.
Fast-setting concrete (like Quikrete Fast-Setting) is ideal for fence posts because it sets in 20-40 minutes and reaches full strength in 4-6 hours. This lets you continue building the same day. Regular concrete works but requires 24-48 hours before attaching fence panels.
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