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Fence Post Spacing Calculator

Each run in even bays, none wider than you allow — the spacing to mark out and the posts it takes.

An estimate — mark the first and last posts, then measure the bays between them.

100' · 1200 in · 100 ft · 30.48 m

100 ft

This page recalculates as you type. There is no Calculate button.

Answer

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Widest post spacing

7' 8 5/16" on center

100 ft of fence · 13 bays · 14 posts in holes 42" deep

Posts 14 posts
Panels 13 panels
Fence, gates left out 100 ft
Concrete 38 × 50 lb fast-setting
Gravel under the posts 8 × 50 lb bags (0.5 ft³)
Ticked items cost $2,470.91
More numbers
Post holes 42" deep, 10" across
DrawingThe project drawn to scale. Run 1: 100' × 6'.100'6'Run 1

Buying noteCall 811 a few business days before you dig. It is the free national before-you-dig service: the utilities mark their lines, and every post hole needs it.
Buying noteYour frost depth is not set. Where the ground freezes, a post set above the frost line heaves: ask your building department for the depth (IRC Table R301.2(1)) and type it under Assumptions — every hole follows it.

Breakdown

Run or gate Measurements Qty Length Share
Run 1 100' Add ×1 100 ft

What to buy

Buying noteCall 811 a few business days before you dig. It is the free national before-you-dig service: the utilities mark their lines, and every post hole needs it.
Buying noteYour frost depth is not set. Where the ground freezes, a post set above the frost line heaves: ask your building department for the depth (IRC Table R301.2(1)) and type it under Assumptions — every hole follows it.

Ways to buy the concrete

The bags for every post hole together, by the shape of the holes. Every way is worked out; pick the one you will buy.

38 × 50 lb fast-setting Bags 38 Left over 0.15 ft³ Weight 1,900 lb Cost $303.24 Reference price $7.98. Type your store's.

Shopping list

12 12 × 9 ft $515.16 Reference price $4.77. Type your store's.
2 2 × 9 ft $85.86 Reference price $4.77. Type your store's.
13 panels, 6 × 8 ft $1,430.13 Reference price $110.01. Type your store's.
14 caps $92.68 Reference price $6.62. Type your store's.
38 38 × 50 lb fast-setting $303.24
8 8 × 50 lb bags (0.5 ft³) $43.84 Reference price $5.48. Type your store's.
Ticked items $2,470.91

Untick what you already have. Lumber is priced by the foot, beside its row; the concrete's bags are priced in the table above.

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How this was worked out

Every number below is yours. Each constant links to the row where you can change it.

Run 1 100' 100 ft
Posts 13 bays in 1 runs: 12 line + 2 end + 0 corner + 0 gate 14 posts

Change:Post spacing, vinyl panels

How deep a post goes 0.5 × 72" out of the ground, or the frost depth 0" where deeper 36" + 6" = 42"

Change:Post in the ground, share of its height aboveYour frost depthGravel in the bottom of a hole

Line posts, length 72" + 36" = 108" 12 × 9 ft
End posts, length 72" + 36" = 108" 2 × 9 ft
Concrete, each line post (π ÷ 4 × 10" × 10" − 5" × 5") × 32 1/2" 1.007 ft³ × 12 = 12.084 ft³

Change:Hole across, vinyl postConcrete stops under the ground

Concrete, each end post (π ÷ 4 × 10" × 10" − 5" × 5") × 32 1/2" 1.007 ft³ × 2 = 2.014 ft³

Change:Hole across, vinyl postConcrete stops under the ground

Bags of concrete 14.098 ft³ ÷ 0.375 ft³ 37.59 → 38 × 50 lb fast-setting

Change:Yield, 50 lb fast-setting bag

Gravel under the posts π ÷ 4 × 10" × 10" × 6" × 12 + π ÷ 4 × 10" × 10" × 6" × 2 3.818 ft³ → 8 × 50 lb bags (0.5 ft³)

Change:Gravel in the bottom of a hole

Panels one panel to each of the 13 bays, the last of a run cut to fit 13

Change:Post spacing, vinyl panels

What it comes to 12 × 9 ft × $4.77/ft + 2 × 9 ft × $4.77/ft + 13 × $110.01 + 14 × $6.62 + 38 × $7.98 + 8 × $5.48 $2,470.91

Assumptions

Every one of these is editable. Change one and the answer changes with it.

Assumption Value Confidence
Post spacing, vinyl panelsA 6×8 vinyl privacy panel (Veranda Linden) is 91 in wide between 5 in posts: 96 in on center. Freedom's kit instructions space posts at the panel's width plus the post's. ~ in Derived or single-supplier
Post in the ground, share of its height aboveQuikrete Fast-Setting Concrete Mix spec sheet, section 5: a post hole one half as deep as the post stands above ground. Quikrete's Setting Posts sheet says the same as one third of the post's length, and so does Home Depot's chain link guide for its posts. ratio From a data sheet or an agency document
Your frost depthYour frost depth, from your building department (IRC Table R301.2(1) is filled in locally). 0 means not given: every hole is then as deep as the post's own rule. Typed in, no hole stops above it. ≈ in Trade convention
Gravel in the bottom of a holeQuikrete Setting Posts, step 2: 6 in of gravel or crushed stone in the bottom of the hole, for drainage. in From a data sheet or an agency document
Concrete stops under the groundQuikrete Setting Posts, steps 4 and 6: fill the hole to 3-4 in below the top, then finish with soil. The middle of the range. in From a data sheet or an agency document
Hole across, vinyl postFreedom vinyl fence kit instructions, p. 2: a 10 in hole for a 5×5 post. Veranda's instructions say the same. in From a data sheet or an agency document
Yield, 50 lb fast-setting bagQuikrete Fast-Setting Concrete Mix spec sheet. ft³/bag From a data sheet or an agency document

How far apart to set fence posts

Divide each run into equal bays no wider than the spacing you allow, and the bays round up. 100 feet at no more than 8 feet is 12½ bays, so 13 bays of 7' 8 5/16" on center, and 14 posts. Thirteen bays of 8 feet would overshoot by 4 feet; twelve would leave one bay 4 feet wider than the rest. Even bays put every rail on the same cut and every post the same distance from the next.

RunBays at 8 ft or lessOn centerPosts
50 ft77' 1 11/16"8
60 ft87' 6"9
75 ft107' 6"11
100 ft137' 8 5/16"14
150 ft197' 10 3/4"20

Which spacing

A wood fence on 2×4 rails is set no more than 8 feet apart, the length of the rail that spans a bay; wider than that a rail sags under the pickets, which is what builders say and what Inch Calculator and Omni both use — no standard gives the figure. Chain link line posts may be 10 feet apart. A panel fence has no choice: its posts stand a panel apart, 96 inches for an 8 foot vinyl or wood panel and 72½ for a 6 foot aluminum one. Split rail stands a rail apart, about 10 feet 3 inches for an 11 foot rail. Each is a figure under Assumptions you can change.

Several runs

Every run is divided on its own, from corner to corner or from end to gate, because a corner post is where both runs stop. A back yard of 50, 100 and 50 feet is 7, 13 and 7 bays — 27 — and 28 posts, the corners counted once.

Marking it out

Set the end and corner posts first and pull a string between them at post height. Measure the on-center spacing along the string from one end, mark each post, and dig. Measuring each bay from the last post adds up its errors; measure every mark from the same end. For the gaps between pickets — the even spacing a spacer block is cut to — use the picket fence calculator. We are not connected with any maker, store or supplier named here.