Calculate fence materials, posts, and pickets
A fence calculator estimates posts, rails, pickets, and materials for wood, vinyl, or metal fencing. Accurate calculations ensure consistent spacing and professional results.
The fence estimate removes gate openings from the perimeter first and works on what is left. Posts are the remaining length divided by the post spacing, rounded up, plus one, with two extra posts for each gate. Rails are counted in 8-foot sections, two rails on a 4-foot fence and three on a 6-foot or 8-foot fence. Privacy pickets are counted by dividing the length by the picket width with no gaps, while shadowbox and picket styles allow for their gaps.
Posts = (Perimeter / Post Spacing) + 1; Rails = Posts × Rails Per Section
| Calculation | Expression | Result |
|---|---|---|
| Fence length after one 4 ft gate | 120 ft − 4 ft | 116 ft |
| Posts at 8 ft spacing | (116 ÷ 8, rounded up) + 1 + 2 gate posts | 18 posts |
| Rails for a 6 ft fence | (116 ÷ 8, rounded up) × 3 rails | 45 rails of 8 ft |
| Privacy pickets (5.5 in wide) | 116 ft × 12 ÷ 5.5, rounded up | 254 pickets |
6-8 feet: Standard for most wood fences. 6 feet: Better for tall fences or windy areas. 8 feet: Common for vinyl and metal panels. Never exceed 8 feet for structural integrity.
General rule: 1/3 of total post length underground. 6' fence = 8' post with 2' buried. In cold climates, go below the frost line (typically 36-48"). Use 9-10' posts for 6' privacy fence.
One 50 lb bag per post for 4×4 posts. Two bags for 6×6 posts. Fast-setting concrete is convenient for DIY. Use post mix that doesn't require mixing for quickest install.
Calculate: Fence length (inches) / (picket width + gap). Standard 6" picket with 1/4" gap: About 18 pickets per 10 feet of fence. Buy 10% extra for defects and cuts.
4-foot fence: 2 rails. 6-foot fence: 2-3 rails. 8-foot fence: 3 rails. Rails should be 2×4 for most fences, 2×6 for heavy fences. Top rail prevents warping.
Pre-made panels: Faster, more consistent, limited customization. Build on-site: Adapts to slope, custom spacing, more labor. Panels work for level ground; build on-site for slopes.
Eighteen at 8-foot spacing: the 4-foot gate leaves 116 feet, 116 ÷ 8 = 14.5 rounds up to 15 sections, so 16 line posts, plus 2 extra posts to hang the gate.