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Fence Calculator: Posts, Rails, Pickets and Concrete
Plan a wood privacy or picket fence: enter the length and style to get the number of posts, rails, pickets and bags of concrete, and a material cost.
How many fence posts do I need?
Subtract the gate openings from the total length, divide by the post spacing and round up to get the number of sections. You need one more post than sections, plus one extra post for each gate. A 150 ft fence with one 4 ft gate has 146 ft of fence, which is 19 sections at 8 ft, so 21 posts.
Corners and ends always need a post, so if your fence has several straight runs, it is more accurate to calculate each run separately and add them up.
Rails and pickets
Fences up to 5 ft tall usually have 2 rails per section; 6 and 8 ft fences need 3 rails to stop the pickets from warping. For pickets, divide the fence length in inches by the picket width plus the gap. A privacy fence has no gap; a classic picket fence often has a gap about the width of a picket. We add 5% for splits and bad boards.
How deep should fence posts be?
A common rule is to bury one third of the post's above-ground height, and at least 24 inches, deeper still below your area's frost line. So a 6 ft fence needs posts at least 24 to 30 inches deep, which means buying 8 ft posts. Holes are usually about 3 times the post width: 10 to 12 inches for a 4 × 4 post.
A 50 lb bag of fast-setting concrete fills about 0.375 cu ft. Before digging, call 811 to have underground utility lines marked for free, and check property lines, HOA rules and permit requirements.
Frequently asked questions
How many fence posts do I need for 100 feet?
With posts 8 ft apart, 100 ft of fence has 13 sections and needs 14 posts, plus one more for each gate.
How many bags of concrete per fence post?
For a 4 × 4 post in a 10 in hole 24 in deep, about 2½ bags of 50 lb fast-setting concrete, so buy 3 per post.