Fence Picket Spacing Calculator
Find the exact gap between pickets, or how many pickets you need, before you cut a single board.
Why fence picket spacing matters
Picket spacing is the small detail that decides whether a fence looks professional or improvised. A gap that drifts from a quarter inch at one end to a full inch at the other is obvious from the street, and it usually means the last picket has to be ripped down to fit. Planning the spacing first removes that problem. It also affects privacy, airflow, wind load, material cost, and whether the fence keeps small pets and children where you want them.
Wood moves, too. Boards swell in damp weather and shrink in dry heat, so a gap that looks perfect on installation day can close up or open wide later. Leaving a deliberate gap gives the wood room to expand and lets rain drain away instead of rotting the bottom rail. This guide covers how to use the calculator above, the math behind it, and practical advice for different fence styles.
How to use the fence picket spacing calculator
- Pick a mode. Choose “Find gap spacing” if you already know how many pickets you bought. Choose “Find picket count” if you know the gap you want and need a shopping list.
- Enter the fence length. Measure from the inside face of one post to the inside face of the next. Use the unit menu if you measured in meters or inches.
- Enter the picket width. Use the real width, not the nominal size. A board sold as “1×4” is usually closer to 3½ inches wide.
- Add the last input. That is the number of pickets in the first mode, or your target gap in the second.
- Choose a layout. Most panels run between two posts, so the default adds a gap at both ends. Pick the second layout if the first and last pickets sit flush with the ends.
- Press Calculate. You get the gap in decimals and in the nearest sixteenth of an inch, plus a scaled drawing of your fence section.
The manual formula for picket spacing
If you prefer pencil and paper, the math is simple. Total fence length equals the space taken by the pickets plus the space taken by the gaps. With a gap at both ends, a run of n pickets has n + 1 gaps.
Example: a 96 inch panel with 20 pickets that are 3.5 inches wide. The pickets cover 70 inches, which leaves 26 inches of gap space. Divide by 21 gaps and each one is about 1.24 inches, or roughly 1¼ inches.
Working backward to count pickets
When you choose the gap yourself, flip the formula:
Round down to a whole number, because you can’t install part of a board, then recalculate the gap with that whole number. The calculator does this for you and shows the small adjustment so every gap stays identical.
If the first and last pickets sit on the ends of the run, there is one fewer gap than pickets. Use n − 1 as the divisor and add the gap to the length in the second formula.
Spacing tips for different fence types
Privacy fences
A true privacy fence has little or no gap. Many builders still leave about 1/8 inch so boards can swell without buckling. Another option is board-on-board, where a second layer of pickets covers the gaps behind. It uses roughly 20 to 30 percent more boards, so run the numbers before you order.
Standard picket fences
Classic garden pickets look best when the gap is close to half the picket width, about 1½ to 2 inches for a 3½ inch board. Keep the gap narrower than the board so the fence reads as a solid rhythm rather than scattered sticks. If you have pets or toddlers, stay under 4 inches and check your local code.
Semi-privacy fences
Semi-privacy designs use a gap of about ½ to 1 inch. They block direct views but let wind pass, which reduces the load on posts during storms. This spacing is popular in windy regions and along pool areas where airflow matters.
Sloped yards
On a slope, either step the panels or rack them to follow the ground. For racked panels, measure the length along the rail rather than the horizontal distance, then use the calculator with that number. Stepped panels are calculated one panel at a time.
Common mistakes to avoid
- Using nominal board sizes instead of measured widths.
- Forgetting that wet lumber shrinks as it dries.
- Measuring from post centers instead of the visible opening.
- Spacing by eye instead of cutting a spacer block to the calculated gap.
Once you have your gap, cut a scrap board to that exact width and use it as a spacer for every picket. It is the fastest way to keep the whole fence consistent.
Frequently asked questions
What is the standard gap between fence pickets?
For decorative picket fences, 1½ to 3 inches is typical. Semi-privacy fences use ½ to 1 inch, and privacy fences use up to 1/8 inch or overlap boards. Pick the gap that matches your purpose and local code.
How do I calculate fence pickets for a sloped yard?
For a racked fence, measure along the sloped rail and use that length in the calculator. For a stepped fence, calculate each level panel separately and add the totals.
How many pickets do I need for 100 feet of fence?
Enter 100 ft, your picket width, and your gap in the second mode. For 3½ inch pickets with a 1½ inch gap, you need about 240 pickets. Add 5 to 10 percent for cuts and defects.
Should the gap be the same at the posts as between pickets?
Yes, if you want a uniform look. Use the “between two posts” layout so the end gaps match the rest. Some builders prefer a pre-set gap against posts, which you can handle by shortening the length you enter.
Do I need to leave a gap at the bottom of the fence?
A 1 to 2 inch clearance above the ground keeps wood dry and prevents rot. It also makes mowing and trimming easier. Remember that it affects privacy and pet containment.