★ CONSTRUCTION · FENCES · POST SPACING
14 posts, 14 bags, $168.00 — 100 ft of fence at 8 ft spacing. The chart covers wood, vinyl, chain-link, and pool fences, and the calculator works out posts, concrete, and cost for your run. Enter your length and spacing to work out yours.
Every fence is a row of posts with panels, rails, or mesh between them. The chart gives the recommended post spacing, post size, and concrete per post for eight common fence types. The calculator works out your run: intervals, posts, bags of concrete, and post cost — from the length and spacing you enter.
Fence posts stand in the ground and hold the panels, rails, or mesh between them. How far apart they stand depends on the fence: wood and vinyl panels are stiff and heavy, so their posts stand 8 ft apart; chain-link and split rail are lighter and more flexible, so their posts can stand 10 ft apart; pool fences stand 6 ft apart because the code for pool barriers wants a tighter fence. The post size follows the fence too: wood posts are 4×4, vinyl posts are hollow 5×5, chain-link posts are 2⅚ in steel, and pool fence posts are 2×2 aluminum. Concrete holds the post in the ground: 1 bag per post for wood, chain-link, and pool fences, 2 bags for vinyl, because a hollow vinyl post takes more mix to fill and set.
| Fence type | Height | Post spacing | Post size | Concrete per post |
|---|---|---|---|---|
| Wood privacy | 6 ft | 8 ft | 4×4 | 1 bag |
| Wood shadowbox | 6 ft | 8 ft | 4×4 | 1 bag |
| Wood picket | 4 ft | 8 ft | 4×4 | 1 bag |
| Ranch rail | 4 ft | 8 ft | 4×4 | 1 bag |
| Split rail | 3 ft | 10 ft | 4×4 | 1 bag |
| Chain-link | 4–6 ft | 10 ft | 2⅚ in steel | 1 bag |
| Vinyl privacy | 6 ft | 8 ft | 5×5 | 2 bags |
| Pool / aluminum | 4 ft | 6 ft | 2×2 aluminum | 1 bag |
At the defaults — 100 ft of fence, 8 ft spacing, 1 bag per post, $12 a post — the fence needs 13 intervals and 14 posts, 14 bags of concrete, and $168.00 of posts. The rule is: posts = intervals + 1, always round intervals UP. 100 ÷ 8 = 12.50, which rounds up to 13 intervals, and 13 + 1 = 14 posts. The last span is 4 ft: 12 full 8 ft spans are 96 ft, and the final span covers the last 4 ft.
| Case | Intervals | Posts | Bags | Post cost | Last span |
|---|---|---|---|---|---|
| Default (100 ft, 8 ft spacing, 1 bag, $12/post) | 13 | 14 | 14 | $168.00 | 4 ft |
| 50 ft fence | 7 | 8 | 8 | $96.00 | 2 ft |
| 200 ft fence | 25 | 26 | 26 | $312.00 | 8 ft |
| 6 ft spacing | 17 | 18 | 18 | $216.00 | 4 ft |
| 10 ft spacing | 10 | 11 | 11 | $132.00 | 10 ft |
| 150 ft fence | 19 | 20 | 20 | $240.00 | 6 ft |
| 2 bags per post (vinyl) | 13 | 14 | 28 | $168.00 | 4 ft |
Setup: fence length 100 ft, post spacing 8 ft, 1 bag of concrete per post, $12 per post.
Line 1 — the intervals. 100 ÷ 8 = 12.50, which rounds UP to 13 intervals. Never round down: 12 intervals would only cover 96 ft, 4 ft short.
Line 2 — the posts. 13 intervals + 1 = 14 posts. One post at each end, plus one between each pair of intervals.
Line 3 — the last span. 12 full spans of 8 ft are 96 ft, so the last span is 100 − 96 = 4 ft. The final post stands 4 ft from the one before it, not 8 ft.
Line 4 — the concrete. 14 posts × 1 bag = 14 bags.
Line 5 — the post cost. 14 posts × $12.00 = $168.00.
Line 6 — the check. 14 posts make 13 intervals; 13 intervals at up to 8 ft cover 104 ft, which is at least the 100 ft of fence, and the last interval is the short one. The count is right when the intervals cover the whole length and the last span is shorter than the spacing.
Reverse: 20 posts at 8 ft spacing cover 19 × 8 = 152 ft of fence; 10 posts cover 9 × 8 = 72 ft; a $500 budget at $12.00 a post buys 41 posts ($492.00; 42 posts cost $504.00, over budget) and covers 40 × 8 = 320 ft.
50 ft fence: 50 ÷ 8 = 6.25, rounds up to 7 intervals, so 8 posts, 8 bags, $96.00. 200 ft fence: 200 ÷ 8 = 25 exactly, so 25 intervals and 26 posts, 26 bags, $312.00 — no rounding needed when the length divides evenly.
6 ft spacing: 100 ÷ 6 = 16.67, rounds up to 17 intervals, so 18 posts, 18 bags, $216.00. 10 ft spacing: 100 ÷ 10 = 10 exactly, so 10 intervals and 11 posts, 11 bags, $132.00. Closer spacing costs more posts: 6 ft spacing needs 7 more posts than 10 ft spacing over the same 100 ft.
150 ft fence: 150 ÷ 8 = 18.75, rounds up to 19 intervals, so 20 posts, 20 bags, $240.00. 2 bags per post (vinyl): the posts stay at 14, but the concrete doubles to 28 bags; the post cost stays at $168.00.
Reverse — the other way round: 20 posts cover 152 ft at 8 ft spacing; 10 posts cover 72 ft; a $500 budget buys 41 posts and covers 320 ft.
The model assumes a straight run of fence on flat ground, with evenly spaced posts and one bag of concrete per post. It assumes the spacing in the chart is right for your fence, but local building codes and pool codes can demand closer spacing, deeper posts, or a different post size — check the code before you buy. It leaves out gates, which need their own posts and hardware, and corners, which usually get a bigger post. It leaves out slopes: on a slope the posts step down and the spacing is measured along the slope, so a hilly run needs more posts than a flat run of the same length. It leaves out the panels, rails, and mesh themselves, and the concrete cost — only the post count, the bags, and the post cost are worked out here. With a fence length of 0 ft the answer is 0 intervals and 1 post, 1 bag, $12.00 — the starting post, with nothing after it. With a 5 ft fence at 8 ft spacing the answer is 1 interval and 2 posts, 2 bags, $24.00. Rounding convention: all figures are computed from unrounded values and rounded only for display — posts and bags are whole numbers, money to cents, so a figure worked out from the rounded numbers can differ by a cent from the figure shown.
| Output | Formula | What it means |
|---|---|---|
| Intervals | ceiling of fence length ÷ spacing | 13 (100 ÷ 8 = 12.50, rounded up). |
| Posts | intervals + 1 | 14 (one post at each end, plus one per interval). |
| Concrete bags | posts × bags per post | 14 bags. |
| Post cost | posts × cost per post | $168.00. |
| Last span | fence length − (intervals − 1) × spacing | 4 ft (12 full 8 ft spans = 96 ft, last span 4 ft). |
| 20 posts cover | (20 − 1) × spacing | 152 ft of fence. |
| 10 posts cover | (10 − 1) × spacing | 72 ft of fence. |
| $500 budget buys | floor($500 ÷ cost per post) | 41 posts ($492.00; 42 posts cost $504.00). |
| $500 budget covers | (41 − 1) × spacing | 320 ft of fence. |
| 50 ft fence | same model, L = 50 | 8 posts, 8 bags, $96.00. |
| 200 ft fence | same model, L = 200 | 26 posts, 26 bags, $312.00. |
| 6 ft spacing | same model, s = 6 | 18 posts, 18 bags, $216.00. |
| 10 ft spacing | same model, s = 10 | 11 posts, 11 bags, $132.00. |
| 150 ft fence | same model, L = 150 | 20 posts, 20 bags, $240.00. |
| 2 bags per post | same model, b = 2 | 14 posts, 28 bags, $168.00. |
The math is exact for the numbers you enter: intervals are the fence length divided by the spacing rounded up, posts are intervals plus one, bags are posts times bags per post, and post cost is posts times cost per post. What the model cannot do is know your ground: check the spacing in the chart against your local code, because pool fences and some towns demand closer spacing, and check the post depth, because frost lines and wind loads decide how deep a post must go, not this chart. It assumes a straight, flat run with no gates and no corners. It leaves out the panels, rails, mesh, and hardware, and the cost of the concrete itself. For the cost of a whole fence, see fence cost calculator; for how much concrete a job needs, see concrete calculator.
Bright Side Kit. "Fence Post Spacing Chart: Posts, Bags & Cost Guide 2026" https://brightoolbox.com/fence-post-spacing-chart/ Accessed October 25, 2026.14 posts at 8 ft spacing. 100 ft divided by 8 ft is 12.50, which rounds up to 13 intervals, and posts are intervals plus one: 13 + 1 = 14. At 6 ft spacing it is 18 posts, and at 10 ft spacing it is 11 posts. You also need 14 bags of concrete and $168.00 of posts at $12 a post.
Because a fence line needs a post at both ends. Each interval is the gap between two posts, so 13 gaps have 14 posts around them — one at the start, one at the end, and one between each pair of gaps. Dividing 100 by 8 gives 12.50, which is the number of gaps before rounding, not the number of posts.
8 ft for most wood and vinyl fences, 10 ft for chain-link and split rail, 6 ft for pool fences. The chart gives the recommended spacing by fence type: wood privacy, shadowbox, picket, and ranch rail all take 8 ft; split rail and chain-link take 10 ft; vinyl privacy takes 8 ft; pool and aluminum fences take 6 ft. Closer spacing is stronger but costs more posts.
1 bag per post for wood, chain-link, and pool fences; 2 bags for vinyl privacy posts. Vinyl posts are hollow and wider (5×5), so they take twice the concrete. For 100 ft at 8 ft spacing that is 14 bags for wood and 28 bags for vinyl. One bag is the usual 50 lb bag of fast-setting mix.
152 ft at 8 ft spacing. 20 posts make 19 intervals, and 19 × 8 ft = 152 ft. With 10 posts you get 9 intervals, or 72 ft. The rule works backwards too: posts minus one, times the spacing, is the fence length.
41 posts, or 320 ft at 8 ft spacing, at $12 a post. $500 divided by $12 is 41.67, so 41 posts fit the budget at $492.00; 42 posts cost $504.00, over budget. Those 41 posts make 40 intervals of 8 ft, which is 320 ft of fence — before concrete and panels.
It still needs 2 posts. A 5 ft fence at 8 ft spacing is 1 interval (5 ÷ 8 rounds up to 1) and 2 posts, one at each end, with the single span 5 ft long instead of 8 ft. A fence of 0 ft needs 1 post and no intervals — the starting post, with nothing after it.