How to use the fence calculator
- Enter the total fence length.
- Enter the post spacing. 8 ft is common for wood fences with 8 ft rails.
- Enter the number of gates and their width.
- Enter rails per section and the picket width and gap.
- Choose the post size and enter the hole diameter and depth you will dig.
Mark gate positions on your plan before you count posts, because every gate needs posts of its own. That is a step Decoratoradvice suggests doing first.
Fence formulas
Fenced run = total length − gate widths
Sections = run ÷ post spacing, rounded up
Posts = sections + 1 + one per gate
Rails = sections × rails per section
Pickets = run ÷ (picket width + gap), rounded up
Concrete per hole = hole volume − post volume
Bags = posts × concrete per hole ÷ bag yield
The bag count uses 0.375 cu ft per 50 lb bag, the yield QUIKRETE publishes for its Concrete Mix.
Worked example
A 100 ft fence, posts 8 ft apart, no gates, two rails, 5½ in pickets with ½ in gaps, 4 × 4 posts in 10 in holes 24 in deep:
Sections: 100 ÷ 8 = 12.5, so 13
Posts: 13 + 1 = 14
Rails: 13 × 2 = 26
Pickets: 1,200 in ÷ 6 in = 200
Concrete per hole: π × 5² × 24 − 3.5² × 24 = 1,591 cu in = 0.92 cu ft
Bags: 14 × 0.92 ÷ 0.375 = 34.4, so 35 bags of 50 lb
With one 4 ft gate, the fenced run is 96 ft: 12 sections and still 14 posts, because the gate adds its own post.
Tips
- Set the corner, end and gate posts first, then run a string line between them to place the line posts.
- Gate posts carry more load; use a deeper hole and a larger post if your design allows.
- Hole size and depth depend on fence height, soil and frost depth. Follow local practice or code.
- Price lumber by the piece, or by the board foot for hardwood, with the board foot calculator.
Common mistakes
- Forgetting the end post. 13 sections need 14 posts.
- Not subtracting gates from the picket run.
- Holes barely wider than the post. There is no room for concrete; the calculator warns you.
Frequently asked questions
How many posts do I need for a 100 ft fence?
At 8 ft spacing, 14 posts with no gates. Add one post for each gate.
How far apart should fence posts be?
The rail length usually sets it: with 8 ft rails, posts go 8 ft apart on centre. Shorter spacing makes a stiffer fence and suits heavier panels.
How many bags of concrete per fence post?
It depends on the hole. A 10 in hole 24 in deep around a 4 × 4 post holds about 0.92 cu ft, which is about 2½ bags of 50 lb Concrete Mix.
How many pickets do I need per 8 ft section?
96 in ÷ (5.5 + 0.5) = 16 pickets with ½ in gaps, or 18 with no gaps (rounded up).
Do I need gravel under fence posts?
Some builders put a few inches of gravel in the bottom of the hole for drainage. The gravel calculator works out the volume.
Can I use the same calculator for a deck railing?
The posts and rails follow similar logic, but deck railings have height and load requirements. Plan the deck with the deck calculator and follow your local code for railings.
Key takeaways
- Sections = run ÷ spacing, rounded up; posts = sections + 1, plus one per gate.
- Pickets = run ÷ (picket width + gap).
- Concrete per post is the hole volume minus the post.
- Mix concrete with the concrete calculator for footings and pads.
Sources
- QUIKRETE Concrete Mix (No. 1101) data sheet: 50 lb bag yield.