Fence Calculator

How to Use This Calculator

Enter your total fence length in feet: this is the full perimeter run you want to fence, not individual sides. Set post spacing: 8 feet is standard for most wood fences. Use 6 feet for shorter fences or soft ground. Set rails per section: 2 for fences under 5 feet, 3 for 6-foot privacy fences. Enter picket width in inches: a dog-ear cedar or pressure-treated picket is typically 3.5 inches for a 1×4, or 5.5 inches for a 1×6. Set gap to 0 for a privacy fence with no gaps. For a picket fence with spacing, enter the gap width (typically 1 to 3 inches). For board-on-board fencing where boards overlap, enter a negative gap (overlap amount). Use the quick-pick buttons for common fence styles.

How to Calculate Fence Materials

Formulas: Posts = (Fence Length / Post Spacing) rounded up, plus 1 end post. Pickets = (Fence Length in inches) / (Picket Width + Gap) rounded up. Rail linear feet = Fence Length × Number of Rails. Concrete bags = Posts × 2 (two 60-lb bags per post fills a standard 8-inch diameter hole at 24-inch depth; deeper or wider holes require 3 bags).

Example: 100-foot privacy fence, 8-ft post spacing, 3 rails, 3.5-inch boards, no gap. Posts = ceil(100 / 8) + 1 = 14 posts. Pickets = ceil(100 × 12 / 3.5) = 343 pickets. Rail feet = 100 × 3 = 300 linear feet. Concrete = 14 × 2 = 28 bags.

For board-on-board, enter a negative gap. With 5.5-inch boards and a 1-inch overlap (gap = -1): Pickets = ceil(100 × 12 / (5.5 - 1)) = ceil(1200 / 4.5) = 267 boards. Board-on-board uses fewer boards than tight-spaced privacy fencing at the same board width.

Fence Tips

Dig post holes deep enough. Industry standard: 1/3 of total post length in the ground, plus 6 inches below the frost line in cold climates. For a 6-foot fence you need 9-foot posts: 3 feet underground, 6 feet above grade. In frost-prone regions, add the local frost depth to the in-ground portion. Contact your local building department for the frost depth in your area.

Use ground-contact rated pressure-treated lumber for any post section that goes underground. Look for UC4B or UC4A treatment ratings on the tag. Standard deck-grade pressure-treated lumber (UC3B) is rated for above-ground use only and will rot much faster in direct soil contact. The treatment rating is printed on a tag stapled to the post.

Space posts consistently for visual uniformity. Measure from corner post to corner post and divide evenly rather than letting the last section be a short stub. For a 100-foot run at 8-foot spacing, the last section would be 4 feet; adjust to 7.7-foot spacing for uniform sections. Most people never notice the difference from the street.

For concrete in post holes, use fast-setting concrete (Quikrete Fast-Setting or Sakrete) poured dry into the wet hole and soaked with water. No mixing required. Sets in 20 to 40 minutes so posts stay plumb while you work. Two 60-lb bags per post fills a standard 8-inch diameter hole; use three bags for 10-inch diameter holes or holes deeper than 30 inches.

What to Buy

For post material: 4×4 pressure-treated posts rated UC4B (ground contact) in 8-foot or 10-foot lengths. For a 6-foot fence, use 9-foot posts. Home improvement stores stock 8-foot and 10-foot; order 9-foot from a lumber yard if needed or cut 10-foot posts.

For rail material: 2×4 pressure-treated lumber cut to your section length. Precut 8-foot 2×4s work for standard 8-foot post spacing. For custom spacing, buy 10-foot or 12-foot boards and cut to length.

For pickets: dog-ear cedar or pressure-treated pine pickets sold in 6-foot lengths. Cedar costs more but takes stain well and resists rot naturally. Pressure-treated pine is cheaper and durable. Avoid using untreated pine for exterior fence pickets.

For concrete: two 60-lb bags of fast-setting Quikrete or Sakrete per post for a standard 8-inch hole; three bags for a 10-inch hole or deeper installations. Costs about $6 to $9 per post at two bags. Total concrete cost for a 14-post fence: around $90 to $130. This is the cheapest part of the fence and not worth skimping on.

Frequently Asked Questions