About Fence Calculator (Posts, Rails, Pickets & Concrete)
The fence calculator turns a run length into a complete wood-fence shopping list: line posts and sections, rails, pickets, the post length to buy, post-hole dimensions, and the concrete to set every post. Sections come from dividing the run by the post spacing (6 or 8 ft on center) and rounding up; posts are sections plus one, plus one extra post for each gate. Rails follow the style — three per section for a 6-ft privacy fence, two for a typical picket fence, and two or three (your choice) for post-and-rail.
Pickets are counted from the covered width of one picket plus its gap: a standard 5-1/2 in dog-ear picket butted tight for privacy, or spaced 1-1/2 in apart for a classic picket look. Posts follow the trade rule of thumb of burying one-third of the fence height with a 2-ft minimum, and the buy length is rounded up to even-foot stock (8, 10, 12 ft). Each hole is three times the post width in diameter over a 4-in gravel drainage base, and the concrete takeoff nets out the post itself, reporting per-hole and total volume with 60-lb and 80-lb premix bag counts.
How It Works
- Enter the total fence run in feet and pick the style: privacy (3 rails, butted pickets), picket (2 rails, spaced pickets), or post-and-rail (no pickets, 2 or 3 rails per section).
- Set the fence height (3-8 ft) and the post spacing, 6 or 8 ft on center. Closer spacing stiffens the fence but adds posts, holes, and concrete.
- For picketed styles, adjust the picket width and gap if you are not using standard 5-1/2 in pickets; the count comes from the run divided by one picket-plus-gap pitch.
- Add the number of gates. Each gate adds one extra post (a second hinge-side or latch-side post) and one hardware set of hinges and a latch; order gate posts one size heavier where the gate is wide.
- Read off posts, rails, and pickets, the even-foot post length from the 1/3-height bury rule (2 ft minimum), the hole size with its 4-in gravel base, and the concrete: per-hole volume, total volume, and 60-lb and 80-lb bag counts ceiled on the total, which is the buy quantity.
Worked Example
A 100-ft privacy fence, 6 ft high with posts 8 ft on center and 5-1/2 in pickets butted tight, no gates. Sections: ceil(100 / 8) = 13, so 14 posts. Rails: 13 x 3 = 39. Pickets: ceil(100 x 12 / 5.5) = 219. Bury: max(2, 6/3) = 2 ft, so the post is 6 + 2 = 8 ft — already an even stock length. Each hole is 3 x 3.5 = 10.5 in across and 2 x 12 + 4 = 28 in deep including the 4-in gravel base. Concrete fills the 24 in above the gravel minus the post: pi x (5.25/12)^2 x 2 - (3.5/12)^2 x 2 = 1.03 ft^3 per hole, 14 x 1.03 = 14.46 ft^3 total — 25 bags of 80-lb premix (or 33 of 60-lb), about 2 x 80-lb bags per hole.
Formulas
- Sections and posts
sections = ceil(run / spacing); posts = sections + 1 + gates- Rails and pickets
rails = sections x railsPerSection; pickets = ceil(run x 12 / (w + g))- Bury depth and post length
bury = max(2, H / 3); postLength = roundUpEven(H + bury)- Post hole
holeDia = 3 x postWidth; holeDepth = bury x 12 + 4- Concrete per hole and bags
V = [pi x (holeDia/24)^2 - (postWidth/12)^2] x bury; bags = ceil(V x posts / yield)
Standards & References
- Trade practice -- post bury 1/3 of fence height, 2 ft minimum (rule of thumb, not a code table)
- Local frost depth may govern post embedment -- check your AHJ before digging
- Call 811 (US) for utility locates before setting posts
Frequently Asked Questions
How deep should fence posts be set?
The trade rule of thumb is one-third of the fence height with a 2-ft minimum: a 6-ft fence gets 2 ft of bury, an 8-ft fence about 2 ft 8 in. In cold climates the local frost depth often governs instead — a post that stops above the frost line can heave — so check the required embedment with your local building department before digging. The calculator adds a 4-in gravel base below the post for drainage, which is why the hole is dug deeper than the bury.
How many fence pickets do I need per foot?
Divide 12 in by the covered width of one picket — its face width plus the gap to the next one. Standard 5-1/2 in dog-ear pickets butted tight cover 5.5 in each, about 2.2 pickets per foot, so a 100-ft privacy fence needs ceil(1200 / 5.5) = 219 pickets. Spaced 1-1/2 in apart for a picket fence, each covers 7 in and the same run needs only 172. Green pressure-treated pickets shrink as they dry, so butted privacy pickets will open small gaps over the first season.
Should fence posts be 6 or 8 feet apart?
Eight feet on center is the standard bay for wood fences because rails come in 8-ft and 16-ft stock. Six-foot spacing makes a noticeably stiffer fence and is worth it for tall privacy fences in windy sites or where the grade steps frequently, at the cost of roughly a third more posts, holes, and concrete. The calculator charts the 80-lb bag totals at both spacings so you can see the concrete cost of the stiffer layout.
How many bags of concrete per fence post?
For a 4x4 post in a 10-1/2 in hole with 24 in of concrete above the gravel base, the net volume is about 1.03 ft^3 — roughly two 80-lb bags per hole. Buy from the total, not per hole: the total pour divided by bag yield (0.60 ft^3 per 80-lb bag, 0.45 ft^3 per 60-lb) and rounded up once wastes far fewer partial bags than rounding up at every hole. A 14-post privacy run needs about 14.5 ft^3, which is 25 x 80-lb bags bought as a single quantity.
How many rails does a fence need?
Two rails carry a fence up to about 5 ft tall; at 6 ft and above, a third rail keeps pickets from cupping and the mid-span from oil-canning, which is why the privacy style here uses three. Classic picket fences under 4 ft use two. Post-and-rail fences are simply two-rail or three-rail styles by look and stock length, so the calculator lets you choose either for that style.
What extra material does a gate add?
Each gate adds one extra post — gate openings are framed by two posts, one of which would otherwise be shared with the neighboring bay — plus a hardware set of two or three hinges and a latch. The gate leaf itself is usually built from the same picket and rail stock already counted in the run. For gates wider than about 4 ft, upgrade the hinge post to a 6x6 or steel post and set it in a deeper, wider footing than the line posts.