What this calculator does
A picket fence calculator answers a narrower question than a general fencing-materials estimate: given the total run of fence, how many individual pickets, at a chosen width, fit along it with a chosen gap between each one. The gap you type in almost never divides the length exactly, so the useful output is the actual, evenly-adjusted gap that makes a whole number of pickets fit flush from one end of the run to the other.
This sits below the level of a general fence-materials calculator, which totals up posts, rails and boards for a whole job. Picket spacing is specifically about the vertical fence boards themselves and the visible gaps between them, the detail that determines how the finished fence actually looks.
The formula
Divide the fence length by the picket width plus the desired gap to get a first estimate of how many pickets fit, then round down to a whole number so the run is not overshot. With that whole number of pickets fixed, spread whatever length is left over evenly across the gaps between them, which gives an actual gap usually a little wider than the one you asked for.
| Term | Meaning |
|---|---|
| Fence run length | The total length of the fence section being fitted with pickets. |
| Picket width | The width of a single picket (vertical fence board), measured face-on. |
| Desired gap | The gap you would like between adjacent pickets, before rounding. |
| Actual gap | The gap once the picket count is rounded to a whole number and spread evenly across the run. |
The inputs explained
| Field | What to enter |
|---|---|
| Fence run length (m) | The total length of the fence run to be filled with pickets. |
| Picket width (mm) | The width of one picket, measured across its face. |
| Desired gap between pickets (mm) | The gap you would ideally like between pickets; the calculator adjusts this slightly so a whole number fit exactly. |
When to use it
Planning a picket fence before buying materials
Working out the picket count and actual spacing before cutting or buying pickets avoids ending up with an odd narrow gap at one end, or realising halfway through that the desired spacing does not divide the run evenly.
Matching an existing fence section
If a new section needs to visually match pickets already installed elsewhere, plugging in the same picket width and the measured existing gap checks whether the new run, at a different length, comes out with a similarly even, comparable spacing.
Comparing picket width options
Trying a slightly wider or narrower picket at the same desired gap shows how much the picket count and actual spacing shift, which helps pick a width that lands close to a whole number of pickets without much adjustment.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How picket count and actual gap change with fence run length
The same picket width and desired gap, applied to a range of fence run lengths.
| Fence run length | Number of pickets | Actual gap between pickets |
|---|---|---|
| 2 m | 11 | 101.00 mm |
| 3 m | 17 | 91.88 mm |
| 4 m | 22 | 96.19 mm |
| 5 m | 28 | 91.85 mm |
| 8 m | 44 | 93.95 mm |
| 10 m | 56 | 90.18 mm |
How picket count changes with picket width, at a fixed fence run
A fixed 3 m fence run, tried with a range of picket widths.
| Picket width | Number of pickets | Actual gap between pickets |
|---|---|---|
| 70 mm | 19 | 92.78 mm |
| 90 mm | 17 | 91.88 mm |
| 100 mm | 16 | 93.33 mm |
| 120 mm | 14 | 101.54 mm |
| 140 mm | 13 | 98.33 mm |
| 150 mm | 12 | 109.09 mm |
Questions
Why is the actual gap different from the gap I entered?
A whole number of pickets almost never fits a real fence length exactly at the gap you first choose. The calculator rounds the picket count down to the nearest whole number, then spreads the leftover length evenly across the gaps, which usually makes the actual gap a little wider than the one entered.
What if the actual gap comes out much wider than I wanted?
Try a slightly narrower desired gap, or a slightly different picket width; both shift how the fence run divides and can bring the picket count, and therefore the actual gap, closer to what you intended.
Does this include posts and rails as well as pickets?
No. This calculator is scoped specifically to the pickets and the gaps between them. For posts, rails and total board quantities for a full fence or deck run, see the fencing and decking materials calculator linked below.
What happens if the fence is too short for two pickets?
The calculator flags that the run cannot fit at least two pickets at the width and gap entered, since a gap calculation needs at least two pickets to have a gap between them. Try a narrower picket, a smaller gap, or a longer run.
For posts, rails and total board quantities across a whole fence or deck job, see the fencing & decking materials calculator. For how deep to set the posts supporting this fence, see the fence post hole depth calculator.