How the fence calculator works
Your fence length divided by the post spacing gives the number of sections; you need one more post than sections. Each section gets two or three rails. Pickets are counted across the full length with your chosen gap. For the posts, it works out the volume of each hole, subtracts the post itself, and converts that to bags of concrete.
The formula
sections = fence length ÷ post spacing, rounded up
posts = sections + 1
rails = sections × rails per section
pickets = fence length ÷ (picket width + gap) × 1.05
concrete / post = (π × (hole diameter ÷ 2)² − post width²) × hole depth
Tips
- Corners and gates need extra posts. This calculator assumes one straight run. Add a post at every corner and one on each side of a gate, or run each straight section separately.
- Dig below the frost line. Frost heave lifts shallow posts. Across much of Canada that means 4 ft (1.2 m) or more; your municipality can tell you the local depth.
- Check bylaws before you build. Most municipalities limit fence height (often lower in front yards), and some require a permit. Call before you dig to have utility lines marked.
- Treated lumber: use posts rated for ground contact.