Fence calculator
Enter each straight run of fence and any gate, and this lays out the posts, bays, rails, pickets or panels, and the bags of concrete for the post holes, all in feet, inches, and fractions. It runs the same layout math as the CutOnce app, which adds a bay diagram, a picket mark list, and a printable material list.
Updated
Segments
Enter each straight run the way your tape reads: 50 ft, 600, or 40 ft 6-1/2 in. A gate width places one gate centered in that segment; leave it blank for no gate. Up to six segments.
Post holes
- Total length
- 120 ft
- Bays
- 17
- Rails
- 51
- Pickets
- 168
- Gates
- 1
- Concrete bags
- 50 × 80 lb
- Concrete volume
- 1.11 yd³
Bays by size
| Post spacing | Count | In each bay |
|---|---|---|
| 7 ft 1-11/16 in | × 7 | 10 pickets, 2-1/2 in gapPicket centers from the near post: 5-1/4 in, 13-3/16 in, 21-3/16 in, 29-1/8 in, 37-1/8 in, 45-1/8 in, 53-1/16 in, 61-1/16 in, 69 in, 77 in |
| 5 ft 11-7/16 in | × 6 | 9 pickets, 1-13/16 in gapPicket centers from the near post: 4-9/16 in, 11-15/16 in, 19-1/4 in, 26-5/8 in, 33-15/16 in, 41-5/16 in, 48-5/8 in, 56 in, 63-5/16 in |
| 7 ft 6 in | × 4 | 11 pickets, 2-3/16 in gapPicket centers from the near post: 4-15/16 in, 12-9/16 in, 20-1/4 in, 27-15/16 in, 35-9/16 in, 43-1/4 in, 50-15/16 in, 58-9/16 in, 66-1/4 in, 73-15/16 in, 81-9/16 in |
How the layout works
Each segment is one straight run. The calculator divides it into the fewest equal bays that stay at or under your max post spacing, so a 50 ft run at 8 ft max becomes 7 bays of 7 ft 1-11/16 in rather than six 8 ft bays and a 2 ft stub. Posts sit at every bay line, and a corner post is shared by the two segments that meet there.
A gate splits its segment at the gate posts. The post centers sit half a post width outside the clear opening you enter, so a 4 ft gate on 3-1/2 in posts takes 4 ft 3-1/2 in center to center, and the fence on either side lays out on its own. Gate posts are counted once even when a gate lands on a corner.
In pickets mode, each bay gets the fewest pickets whose equal gap stays at or under the max gap, and the mark list gives each picket center from the near post face. In panels mode, the run is walked in full panel pitches (panel plus post), and when the leftover is a post width or less, the last two bays are balanced to the same cut width.
Concrete is one cylinder per post, the hole diameter by the hole depth, summed and converted to bags with the waste you enter. The hole is taken as solid; the post's own volume is not deducted, which leaves a little extra in the mix.
A worked example
Three segments of 50, 40, and 30 ft with a 4 ft gate centered in the 40 ft run, 3-1/2 in posts at 8 ft max, three rails, 5-1/2 in pickets at a 2-1/2 in max gap, and 12 in by 24 in holes filled from 80 lb bags. This is the fence the app's own acceptance test lays out.
| Total length | 120 ft | 50 + 40 + 30 ft |
| Runs beside the gate | 2 × 17 ft 10-1/4 in | (40 ft - 4 ft - 3-1/2 in) / 2 |
| Bays in each of those runs | 3 × 5 ft 11-7/16 in | ceil(214-1/4 in / 96 in) |
| Pickets in a gate-run bay | 9 @ 1-13/16 in | fewest pickets with gap ≤ 2-1/2 in |
| Posts | 19 | bay lines + gate posts, shared corners counted once |
| Bays | 17 | 7 + 3 + 3 + 4 |
| Rails | 51 | 3 rails × 17 bays |
| Pickets | 168 | 9 to 11 per bay × 17 bays |
| Concrete bags | 50 × 80 lb | 19 holes × π × 6² × 24 in, over 0.6 ft³ per bag |
Common stock sizes
The calculator takes actual dimensions, not nominal names. These are the actual widths of the lumber most fences are built from, so a 4x4 post is 3-1/2 in and a 1x6 picket is 5-1/2 in.
| Nominal | Actual width | Typical use |
|---|---|---|
| 4x4 | 3-1/2 in | Post |
| 6x6 | 5-1/2 in | Post, gate post |
| 1x4 | 3-1/2 in | Picket |
| 1x6 | 5-1/2 in | Picket, dog-ear |
| 2x4 | 3-1/2 in | Rail |
| 8 ft panel | 96 in | Prebuilt panel |
Pickets or panels
Pickets mode is a stick-built fence: posts at your max spacing, rails between them, and individual pickets. Panels mode is for prebuilt panels: the post spacing is fixed by the panel width plus one post, and the calculator tells you where the last panels have to be cut. A 50 ft run of 8 ft panels on 3-1/2 in posts takes 5 full bays and two balanced bays of 4 ft 3-1/4 in each, with each cut panel at 3 ft 11-3/4 in, instead of six full bays and a 3 in sliver too narrow for a panel.
8 ft 3-1/2 in × 5 · 4 ft 3-1/4 in × 2
What the app adds
This page lays out the fence from imperial input with one centered gate per segment. The app places a gate anywhere along a segment and takes several per segment, draws an elevation of a typical bay, prints the picket mark list per bay size, carries metric input, adds unit prices for a cost total, hands the post count to the concrete calculator with one tap, and exports the whole thing as a PDF material list.
Common questions
- How many fence posts do I need for 100 feet?
- At 8 ft max spacing, a straight 100 ft run takes 13 bays of 7 ft 8-5/16 in and 14 posts: one more post than bays, because both ends get a post. Corners add a post each, shared by both segments. A gate brings two posts of its own, but the runs on either side re-divide into their own bays, so the total can stay the same: the same 100 ft with a centered 4 ft gate is still 14 posts. Enter the segments and gates and the calculator counts the real post lines.
- How far apart should fence posts be?
- Most wood fences are built at 6 or 8 ft on center, matching 6 and 8 ft rail stock and prebuilt panel widths. Enter that as the max post spacing. The calculator never exceeds it; it shortens every bay in the run equally so the last bay is not a stub. Taller fences, windy sites, and heavy panels favor the 6 ft spacing.
- How many bags of concrete per fence post?
- A 12 in diameter hole 24 in deep holds about 1.57 cubic feet, which is 3 bags of 80 lb mix rounded up for one post, or 6 bags for two. Over a whole fence the rounding happens once on the total: the worked example's 19 posts take 50 bags, not 57. A smaller hole, a smaller bag, or a waste percentage changes the count.
- How many pickets do I need?
- Pickets are figured per bay, not per foot. Each bay's clear span is the post spacing minus one post width, and the calculator fits the fewest pickets whose equal gap stays under your max gap. In the worked example a 5 ft 11-7/16 in bay takes 9 pickets of 5-1/2 in at a 1-13/16 in gap. Multiply by the bays and you have the order; the app prints the picket centers so every bay looks the same.
- How deep should a fence post hole be?
- A common rule is a third of the post's length below grade, and at least 24 in, with the bottom below the local frost line so the post does not heave. The hole is usually about three times the post width across, so 10 to 12 in for a 4x4. Enter the hole size you dig and the calculator gives the concrete for it; confirm the depth with your local code.
Lay it out, then print the list
CutOnce lays out the fence like this page, then draws the bay, prints the picket marks, prices the parts, and hands the post count to the concrete calculator, on the jobsite with no signal.
Free to download, with a 7-day trial of everything. This page counts the parts; the app prints the material list and the mark list you take to the yard and the fence line.
See also