Key Takeaways
- Post count is driven by spacing, not fence length alone
- Picket count depends on picket width plus gap, not section width
- Gates add two posts each and remove their width from the fenceable length
- Most fences use two rails for shorter heights and three for taller ones
- A 10 percent waste allowance covers cuts and damaged pickets
Linear foot is a unit of length equal to 1 foot, used for measuring fence length, board length and other one-dimensional dimensions.
Section in fencing is the span between two adjacent posts. The number of sections determines how many posts and pickets you need.
A fence is simpler than a deck in one way: there is no roof load to engineer. But the material count still depends on several interacting numbers, and getting any one of them wrong means either too much material on the truck or not enough on the truck.
Here is how to work through the calculation.
Start with the fence length
The total fence length is the distance around the perimeter you want to enclose. A straight 100 foot run is the simplest case. Curved or irregular perimeters should be measured along the actual fence line, not as the crow flies.
Post count depends on spacing
Post spacing determines how many sections the fence has, and each section needs a post at each end. The number of sections equals the fence length divided by the post spacing, rounded up.
For a 100 foot fence with 8 foot post spacing:
- Sections = ceil(100 / 8) = 13
- Fence posts = 13 + 1 = 14
Each gate needs two additional posts, one at each side. A fence with one 4 foot gate at 50 feet of fence length has:
- Available fence = 50 - 4 = 46 feet
- Sections = ceil(46 / 8) = 6
- Fence posts = 6 + 1 = 7
- Gate posts = 1 x 2 = 2
- Total posts = 9
Picket count depends on the gap
The number of pickets per section is driven by the picket width plus the gap between them, not by the section width alone. A wider picket with a smaller gap needs fewer pickets per foot of fence.
For a section that works out to 7.69 feet wide, with 5.5 inch pickets and 3/8 inch gaps:
- Picket unit = 5.5 + 0.375 = 5.875 inches = 0.4896 feet
- Pickets per section = ceil(7.69 / 0.4896) = 16
Multiply by the number of sections and add the waste allowance for the total picket count.
Rails connect everything together
Rails run horizontally between posts and carry the pickets. A standard fence uses two rails for shorter heights (under 5 feet) and three rails for taller fences. The total rail count equals the number of sections multiplied by the rails per section.
The waste allowance covers cuts and breakage
Cutting pickets to length and handling them during installation creates some waste. Ten percent is a reasonable allowance for a straightforward fence run. Longer fences with more corners or gates may need slightly more.
A caution worth reading
The numbers above are shopping estimates, not engineering specifications. For anything structural or anything your local building department has an opinion about, use what they require. This site produces material quantities, not engineering drawings.
Once you have your dimensions, the fence calculator turns them into a complete material list with pickets, posts, rails and gates.
Editorial note: This article is reviewed for accuracy and updated regularly. All calculations use standard industry formulas. For the latest density figures, consult your supplier directly.
Frequently asked questions
How many fence posts do I need for 100 feet of fence?
At 8 foot post spacing, 100 feet of fence needs 14 posts (one at each end and one at each section boundary). Add two posts for each gate. The exact number depends on your post spacing and how many gates you are installing.
How do I calculate fence pickets?
Divide the section width by the picket width plus the gap between pickets, then round up. For a 7.69 foot section with 5.5 inch pickets and 3/8 inch gaps, that is 92.25 inches divided by 5.875 inches, which gives about 16 pickets per section. Multiply by the number of sections and add the waste allowance.
How many rails do I need for a 6 foot fence?
A 6 foot fence typically needs 3 rails per section, because the additional height requires a middle rail to keep the pickets stable. Shorter fences under 5 feet can use 2 rails. Check your local building codes for the required number of rails.
How wide should a gate opening be?
Standard pedestrian gates are 3 to 4 feet wide. Vehicle gates are typically 10 to 12 feet wide. Each gate needs two additional posts, one at each side, which reduces the fenceable length by the gate width.