Enter the fence length and height to see how many posts, rails and pickets to buy, the post hole size, and how many bags of fast-setting concrete you need.
Quick answers
Posts = fence length ÷ post spacing, rounded up, plus one, plus one for each gate. A 100 ft fence with 8 ft spacing and one 4 ft gate needs 14 posts.
Quikrete: dig each hole 3 times the post width and 1/3 of the post's total length deep, plus 6 in of gravel. For a 4 × 4 post that is a 10.5 in hole.
A 50 lb bag of Quikrete Fast-Setting Concrete yields about 0.375 cu ft. A 4 × 4 post buried 24 in takes about 3 bags; buried 36 in, about 4 bags.
How to use the fence calculator
Measure the full fence line in feet, including gate openings. For several separate runs, add them up and count each extra run end as a corner.
Choose post spacing. 8 ft is common for wood fences with 8 ft rails; 6 ft makes a stiffer fence.
Leave the post depth on Auto to follow Quikrete's rule, or enter the depth your local code or frost line requires.
Following Quikrete, each hole is 3 × post width across and post depth + 6 in deep, with 6 in of gravel at the bottom. Concrete fills the hole around the post up to 3 in below the ground, which is left for soil or sod. Bags = concrete volume ÷ 0.375 cu ft per 50 lb bag, rounded up per post.
Worked example: 100 ft of 6 ft privacy fence with one gate
100 − 4 ft gate = 96 ft of fence ÷ 8 ft = 12 sections, so 13 posts plus 1 for the gate = 14 posts. Quikrete's rule puts 36 in of each 4 × 4 in the ground, so use 9 ft posts in 10.5 in holes, 42 in deep. Concrete per post: about 1.42 cu ft, so 4 bags per post, 56 bags in total. Pickets: 1,152 in ÷ 5.5 = 210. Rails: 12 sections × 3 = 36.
Bags of fast-setting concrete per post
50 lb bags, hole 3 times the post width, top 3 in left for soil.
Post depth in ground
4 × 4 post (10.5 in hole)
6 × 6 post (16.5 in hole)
24 in
3 bags
6 bags
30 in
4 bags
8 bags
36 in
4 bags
10 bags
Before you dig, call 811 (in the US) so buried utility lines are marked. It is free.
Common questions
How many posts do I need for a 100 ft fence?
With posts every 8 ft, 100 ft is 12.5 sections, which rounds up to 13 sections and 14 posts. Each gate adds a post, because a gate needs a post on both sides. Corners can add one more if the spacing does not land exactly on the corner.
How deep should fence posts be?
Quikrete's rule is 1/3 of the post's total length, which works out to half the height above ground. A 6 ft fence then has 3 ft in the ground and uses 9 ft posts. Many builders use 2 ft for a 6 ft fence with 8 ft posts. In cold climates, go below the frost line your local building department lists, and always call 811 before you dig.
How many bags of concrete per fence post?
Quikrete says two 50 lb bags of Fast-Setting Concrete set a 3 in post in a 9 in hole 30 in deep. For a standard 4 × 4 (3.5 in actual) in a 10.5 in hole, plan on about 3 bags at 24 in deep and 4 bags at 36 in deep. A 6 × 6 post in a 16.5 in hole takes two to two and a half times as much.
How many pickets do I need?
Divide the fence length in inches by the picket width plus the gap. For 100 ft of privacy fence with 5.5 in pickets and no gap: 1,200 ÷ 5.5 = 219 pickets. With a 1.5 in gap: 1,200 ÷ 7 = 172.
How many rails per section?
Many wood privacy fences use 3 rails per section at 6 ft tall and 2 rails at 4 ft or less. Check your local code or HOA rules, and the fence panel maker's instructions if you use panels.