Free Fence Calculator Online

Fence Calculator: Work Out Posts, Rails, and Pickets for a Full Run

A fence calculator takes one measurement anybody can get with a tape measure or a wheel — the total length of the fence run — and turns it into a materials list: how many posts to set, how many horizontal rails to cut, and, for a picket-style fence, how many individual pickets to buy. Everything computes live in your browser as you adjust the length, the spacing between posts, or the picket width, so you can test a few different post spacings before settling on one and heading to the lumber yard.

Posts are the part of a fence project where a small planning mistake gets expensive fast — digging one too few post holes, or spacing them wrong partway down a long run, means either an awkward short section at the end or redigging a hole that's already set with concrete. Working out the full post count from the total run length before the first hole is dug avoids that.

How to Estimate Fence Materials With This Tool

1. Choose a unit for the fence length — feet, meters, or inches — using the toggle above the input card. Note that this unit selector only applies to the length field.
2. Enter the total run length of the fence — the full distance the fence needs to cover, regardless of how many straight sections or corners that involves.
3. Set the post spacing, which is always measured in feet regardless of what unit you picked for the length. The default is 8 feet, a common spacing for wood privacy and picket fencing.
4. Set how many horizontal rails run between each pair of posts. Three rails per section is the default, typical for a standard privacy fence design.
5. If you're planning a picket-style fence, enter a picket width in inches to get a picket count; leave it blank if you're building a solid-panel or non-picket fence style, and the tool will skip that calculation.
6. If pickets aren't butted flush against each other, enter the gap you're leaving between them in inches — this widens each picket's effective footprint and lowers the total picket count needed to cover the same run.
7. Adjust the concrete bags per post if you're using something other than one bag per hole, then read the posts, rails, and pickets (or concrete bags, if you didn't enter a picket width) in the result cards.

Why a Fence Materials List Is Easy to Get Wrong by Hand

• The post count isn't just length divided by spacing. A fence run needs one more post than the number of sections it's divided into — a detail that's easy to drop when doing the division mentally, and one that undercounts posts by exactly one on every run.
• Corners and gates change the math. A fence line with corners technically needs its length measured as the sum of each straight segment, since a corner post serves two segments at once rather than being counted twice — worth working out segment by segment for anything but a single straight run.
• Picket count depends on spacing choices most people don't think about until they're at the lumber yard. Butted pickets with zero gap and pickets with a half-inch reveal between them need meaningfully different quantities to cover the same length, and that gap decision is often made on-site rather than planned ahead of time.
• Concrete for post holes is easy to underestimate. Each post hole needs its own bag or partial bag of premix concrete, and multiplying that per-post figure across a long fence run adds up to a real quantity that's worth knowing before a single trip to the store rather than several.
• Comparing spacing options before committing. Running the same fence length at both a 6-foot and an 8-foot post spacing shows the material tradeoff — tighter spacing means a sturdier fence and more posts, wider spacing means fewer posts but a design that may need heavier rails to avoid sagging.

The Math: From Fence Length to a Full Materials List

Step	Formula	Anchor example (100ft fence, 8ft post spacing, 3 rails/section)
Sections	ceil(length / post spacing)	ceil(100 / 8) = 13 sections
Posts	sections + 1	13 + 1 = 14 posts
Rails	sections x rails per section	13 x 3 = 39 rails
Concrete bags	posts x bags per post	14 x 1 = 14 bags

The "plus one" on the post count is the detail worth internalizing: think of a 100-foot run split into 13 roughly-8-foot sections by 13 fence posts standing between them — except that description is one post short, because it's missing the post at the very start of the run. Thirteen sections require fourteen posts: one at each end, plus one between every pair of adjacent sections. Sections are always rounded up to a whole number too, since a fence can't be built with a fractional section — a run that divides out to 12.5 sections needs 13 full sections' worth of posts and rails, with the last section simply narrower than the rest.

Where a picket width is provided, the picket count follows a similar shape: the fence length in inches is divided by the combined width of one picket plus its gap, then rounded up the same way, since a picket fence can't be built with a fractional picket at the end of the run either.

The Spacing and Width Assumptions Behind These Numbers

The 8-foot post spacing default reflects a common choice for wood privacy and picket fencing, chosen as a balance between the number of post holes you have to dig and the rail's ability to span the gap without sagging over time. It isn't a fixed engineering requirement, though — a taller, heavier privacy fence panel, a fence built in loose or sandy soil, or a design using thinner rail stock often calls for tighter spacing, commonly down around 6 feet, to keep the fence rigid and level over the years. A shorter picket fence with lightweight rails can sometimes stretch to spacing wider than 8 feet without trouble. Local wind-load conditions and the specific fencing material you're using are both worth weighing before locking in a spacing wider or narrower than the default.

Picket width and gap are entirely dependent on the specific fence style and lumber you're buying — there's no single industry-standard picket width the way there's a standard interior door size, since picket fencing ranges from narrow 3.5-inch dog-ear pickets to wide 5.5-inch or 6-inch board-on-board designs. Measuring an actual picket from the batch you plan to buy, rather than guessing, is the difference between a picket count that's close and one that's meaningfully off on a long fence run.

Common Fence-Estimating Mistakes

• Forgetting the "plus one" post. Dividing length by spacing and stopping there — without adding the extra post needed to bookend the run — is the most common way a hand-calculated post count comes up one short.
• Not rounding sections up before multiplying out rails. A run that divides out to a fractional number of sections still needs a full extra section's worth of rails and a full extra post, not a partial one.
• Applying one spacing figure to a fence line with corners. Treating a fence with two 50-foot sides meeting at a corner as one continuous 100-foot run, rather than two separate 50-foot runs each needing their own post-and-a-half math, can miscount posts right at the corner.
• Skipping gate posts and hardware. A gate opening typically needs its own heavier posts and doesn't consume rail or picket material the way a standard section does — this calculator's straight-run math doesn't automatically carve out a gate opening, so subtract that section's material by hand if the run includes one.
• Guessing at concrete instead of using a per-post figure. Skipping the concrete estimate and buying "a few bags" for an unspecified number of holes tends to run short on a long fence line with many posts.

Manual Fence Estimating vs. This Calculator

• Pacing off the yard and guessing. Fast, but post spacing guessed by eye rather than measured tends to drift over a long run, leaving an oddly narrow or wide final section.
• A lumber yard's fence estimator. Many suppliers offer a rough materials estimate tied to their own product line, which is convenient if you've already picked a specific fence panel product but less flexible for comparing spacing options before you've chosen one.
• Sketching the run on paper. Drawing the fence line to scale and marking posts by hand works for a simple straight run, but doesn't scale well to a property with multiple corners and gates without a lot of careful re-measuring.
• This calculator's API. A landscaping quote tool, a property-management app, or any workflow that needs a post-and-rail count generated automatically, rather than entered by hand into a form, can reach the same length-to-materials formula through a metered API call; the API documentation covers the parameters and the JSON it hands back.

Why does the calculator report one more post than I'd expect from dividing length by spacing?

Because a fence run needs a post at both ends as well as one between every pair of sections — a 100-foot run at 8-foot spacing breaks into 13 sections, but connecting those sections takes 14 posts, not 13. The extra post is the one at the very start of the line that's easy to forget when doing the division by hand.

What if my fence has a corner, not just one straight run?

Run each straight segment through the calculator separately using that segment's own length, since the "plus one" logic applies per straight run rather than to the property's total perimeter — a corner post effectively serves as the "plus one" post for both adjoining segments rather than being counted twice.

Do I need to enter a picket width if I'm building a solid panel or chain-link fence?

No — leave the picket width field blank. The calculator only computes a picket count when a width is provided; without one, it reports posts, rails, and concrete bags only, which covers panel-style and other non-picket fence designs.

Is one bag of concrete per post always enough?

Not necessarily — it depends on the post size and hole depth, which is why the concrete-bags-per-post figure is an adjustable field rather than a fixed constant. A larger or deeper post hole may need more than one bag; check your specific post size and local frost-depth requirements, then adjust that field before relying on the bag total.

Related Calculators

Setting fence posts almost always means mixing concrete, and the concrete calculator works out volume and bag counts in more depth for post footings than the flat per-post figure used here. If the fence line needs to be measured out from an irregular property shape first, the square footage calculator can help establish the dimensions of the area being enclosed. And for a property project that includes exterior structures beyond the fence line, the roofing calculator covers the separate area-to-bundle math for a shed or outbuilding roof.