Fence calculator

Before you dig

Three things come before the first hole, and none of them is in a calculator.

• The line. Know where your property ends, from your survey and not from the old fence.
• The rules. A fence has a height limit in most places, and often a setback. Decks.com’s guide to post spacing says the location of a fence should be approved by the building or zoning department. A homeowners’ association may have rules of its own.
• What is underground. 811 is the free national before-you-dig service: contact it a few business days before digging, and the buried utilities are marked with paint or flags.

Post spacing and depth

Posts of a wood fence usually stand 6 to 8 ft apart: Millard Lumber’s guide gives that range as a rule, and Decks.com gives the same, noting that posts set just over 8 ft apart need 10 ft rails. The calculator divides each side into equal sections no wider than the spacing you choose.

For depth, the rule of thumb in Hunker’s and Bob Vila’s guides is a hole a third as deep as the fence is high, 24 in for a 6 ft fence, and three times as wide as the post, 10.5 in for a 4 × 4. Both tie the depth to frost: the bottom of the post belongs below the depth the ground freezes to. That depth is local, so the figure to use is your building department’s. The calculator takes the hole you enter and suggests none.

Fence styles

The posts and the concrete are the same for every style. What changes is what hangs between the posts.

• Privacy. Pickets side by side with no gap: the length of the fence over the width of a picket, rounded up.
• Picket. Pickets with a gap between them. Enter the gap you want at the most. The calculator finds the number of pickets and the exact gap that makes them even: over 100 ft, pickets 3 1/2 in wide at 2 1/2 in or under come to 201, 2.483 in apart.
• Shadowbox. Boards on both sides of the rails, each over a gap of the other side. Enter the gap between the boards of one side.
• Horizontal. Rows of boards from post to post, and no rails.
• Chain link. Fabric and top rail by the foot, tension bands and tie wires by The Home Depot’s installation guide: one band fewer than the fence is feet high wherever the fabric ends on a post, a tie every 24 in of top rail and every 12 in of each line post. Its posts usually stand 10 ft apart.

Rails default to 2 for a fence up to 4 ft and 3 above that; type your own number in the options.

Concrete per post

Each hole is a cylinder less the post that stands in it. A hole 10 in across and 30 in deep around a 4 × 4, which is 3.5 in a side, holds 1.15 cu ft. Quikrete’s data sheet gives the yield of a bag: 0.60 cu ft for 80 lb, 0.45 for 60 lb, 0.30 for 40 lb.

The 14 holes of the example take 16.11 cu ft: 27 bags of 80 lb or 36 of 60 lb. The volumes are added up before the bags are rounded.

Gates and corners

Add each side of the fence as its own line. A corner post is shared by the two sides it joins, so two sides of 50 ft take 15 posts where one straight run of 100 ft takes 14: each side is divided into its own sections.

A gate adds one post and takes the pickets off its width: the example with one 4 ft gate needs 15 posts and 210 pickets. The gate’s own frame, hinges and latch are not counted.

Questions about fences

Sources

• Millard Lumber, Building Wood Fences. As a rule, set fence posts about 6 to 8 ft apart: the spacing depends on the type of fence, the terrain and its purpose. Set the corner or end posts first and stretch a line between them. Read on 9 October 2026.
• Decks.com (Trex), Fence Post Spacing: How Far Apart Should Fence Posts Be?. Wooden fences typically take posts 6 to 8 ft apart; chain-link fences usually 10 to 12 ft. Posts set just over 8 ft apart need 10 ft rails, just under 8 ft take 8 ft lumber. The location of a fence should be approved by the building or zoning department. Read on 9 October 2026.
• Hunker, How Deep To Dig Fence Post Holes. Dig down a third of the height of the post above ground: at least 2 ft for a 6 ft post. Make the hole three times the width of the post. Read on 9 October 2026.
• Bob Vila, Setting Fence Posts: Dos and Don’ts. In part so that posts lodge below the frost line, the usual rule is a hole deep enough for the bottom third of the post: 2 ft for a 6 ft post. The diameter should be three times the width of the post: 12 in for a 4 x 4. Read on 9 October 2026.
• Common Ground Alliance, 811: Before you dig. 811 is the free national before-you-dig service. Contact it a few business days before any digging, including installing a fence, so that the approximate location of buried utilities is marked with paint or flags. Read on 9 October 2026.
• The Home Depot, How to Install a Chain Link Fence. Tension bands: three for each end and gate post and six for each corner post for fences up to 4 ft tall, four and eight up to 5 ft, five and ten up to 6 ft. Tie wire: one for every 24 in of the top rail and one for every 12 in of each line post. A post within every 10 ft run of fence. Fabric is sold in rolls 4, 5 or 6 ft high: buy enough to cover the perimeter less the gate openings. Read on 9 October 2026.
• Quikrete, Concrete Mix (No. 1101), data sheet. A 40 lb bag yields approximately 0.30 cu ft, a 50 lb bag 0.375, a 60 lb bag 0.45, an 80 lb bag 0.60 and a 90 lb bag 0.675. An 80 lb bag takes about 6 pt of water to start with, and 6 to 9 pt in all. Read on 9 October 2026.
• Archtoolbox, Lumber Dimensions: Nominal vs Actual. Surfaced softwood lumber: a 2 x 10 is 1 1/2 x 9 1/4 in and a 2 x 12 is 1 1/2 x 11 1/4 in; a 4 x 4 is 3 1/2 x 3 1/2 in and a 6 x 6 is 5 1/2 x 5 1/2 in; a 1 x 4 is 3/4 x 3 1/2 in and a 1 x 6 is 3/4 x 5 1/2 in. Standard lengths run from 6 to 24 ft in steps of 2 ft. Read on 9 October 2026.

Updated 11 October 2026. How we calculate. Found a mistake? Tell us.