Fence Calculator: Posts, Rails, Pickets and Post Concrete

How to use the fence calculator

1. Pick a style. Privacy / picket is one layer of boards with a gap between them. Use a ⅛ in gap for a privacy fence or a wider gap for a spaced picket fence. Board-on-board has two layers, with the front boards covering the gaps in the back layer. Split rail has posts and rails only.
2. Enter each straight run. A fence along three sides of a yard is three runs. Runs that meet at a corner share the corner post. If the fence closes on itself, turn on Fence closes on itself and the calculator drops the extra end post.
3. Set height, post spacing and gates. Spacing is the maximum distance from the center of one post to the center of the next, usually 6 or 8 ft for wood privacy fences. Each gate adds one post.
4. Check the boards. Use the actual width: a nominal 1×6 picket is 5.5 in wide. The extra percentage covers culls and boards you cut.
5. Set the post holes. The calculator fills in a hole 3× the post width and ⅓ of the fence height deep, plus a 6 in gravel base. You can override both. Turn concrete off if you set posts in tamped soil and gravel.

The result shows posts, rails, boards and bags of concrete for every post hole. It also suggests a post length: the fence height plus the depth set in the ground, rounded up to an even lumber length.

How to calculate fence materials

This is the same counting method as the Lowe’s fencing worksheet. One post per section, one more to end the run and one per gate. Two backer rails per section on a 4 ft fence, three on a 6 ft fence. Pickets equal the length in inches divided by the picket width plus any spacing.

Board-on-board follows the Home Depot cedar fence sheet: space the back boards 4 in apart and nail the front boards over the gaps. With 5.5 in boards, each layer repeats every 9.5 in and each front board overlaps its neighbors by ¾ in on each side.

Fence post concrete calculator: bags per post

QUIKRETE’s post-setting instructions give the rules most fence builders use:

• Make the hole three times the width of the post.
• Make it ⅓ to ½ of the post’s above-ground length deep, plus 6 in.
• Put 6 in of gravel in the bottom for drainage.
• Fill with concrete to 3–4 in below the ground, then finish with soil.

The calculator uses the shallow end of that range (⅓), stops the concrete 3 in below grade and subtracts the volume of the post itself, the same way the concrete bag calculator handles post holes.

Bag yields: 0.30 cu ft for 40 lb, 0.375 for 50 lb, 0.45 for 60 lb and 0.60 for 80 lb. QUIKRETE’s Fast-Setting Concrete Mix data sheet lists the same 0.375 cu ft for a 50 lb bag, so the count works for fast-setting post mix too.

All rows assume 6 in of gravel and concrete stopped 3 in below grade, with no extra added. Buy for the whole fence rather than rounding up hole by hole. Leftover fractions add up across many posts.

Worked examples

100 ft privacy fence, 6 ft tall, one gate

At 8 ft spacing, 100 ÷ 8 = 12.5, so 13 sections. Posts = 13 + 1 + 1 gate = 15 posts. A 6 ft fence takes 3 rails per section, so 39 rails. Pickets: 1,200 in ÷ (5.5 + ⅛) = 213.3, and with 5% extra that is 224 pickets.

The default holes are 12 in wide and 30 in deep: 24 in for the post plus 6 in of gravel. Each takes 21 in of concrete, or 1.23 cu ft after subtracting the 4×4. For 15 posts that is 18.4 cu ft, or 20.2 cu ft with 10% extra: 34 bags of 80 lb or 54 bags of 50 lb. The gravel base is 5.9 cu ft, or 12 bags of 0.5 cu ft. Each post has 6 ft above ground and 2 ft in the ground, so buy 8 ft posts.

The Lowe’s worksheet example: 120 ft

120 ÷ 8 = 15 sections. With one gate that is 15 + 1 + 1 = 17 posts. With 5.5 in pickets butted together, 1,440 ÷ 5.5 = 262 pickets. Set the gap to 0 and the extra to 0% and the calculator returns the same 262.

Board-on-board, 100 ft

With 5.5 in boards and a 4 in gap in the back layer, the layout repeats every 9.5 in. That gives 2 × 1,200 ÷ 9.5 = 252.6 boards, or 266 with 5% extra. That is about 18% more boards than a single-layer privacy fence, in exchange for no see-through gaps as the boards shrink.

Split rail, 200 ft

Culpeper’s split rail sets line posts about 10 ft 3 in apart. 200 ÷ 10.25 = 19.5, so 20 sections and 21 posts. With 3-rail sections that is 60 rails. If one run doesn’t divide evenly, the last section is short and its rails get cut.

Tips before you dig

• Check the property line and buried utilities before you mark the post holes. Many places also set fence height limits and frost-depth rules for footings; local rules override any rule of thumb here.
• Mark gates first. Gate posts take the most load, so place them first, then lay out line posts toward the corners.
• Spacing can come down. If a run is 50 ft at 8 ft spacing, the calculator gives 7 sections. Spacing them evenly at about 7 ft 2 in looks better than six full sections and one short one.
• Split rail and concrete: Culpeper’s instructions say to put 12 in of soil in the bottom of the hole, tamp it, and then pour a concrete collar on top. Never put concrete under the post, or water collects and rots it. The calculator follows that when concrete is on for split rail.
• Three rails on tall fences. The Home Depot sheet puts the top and bottom rails 6 in from the ends of the boards and centers the third rail, which helps keep boards from cupping.

Building a deck next to the fence? The deck calculator counts boards, joists and screws. For gravel along the fence line or a drainage trench, use the gravel calculator.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

• Sections = each straight run ÷ post spacing, rounded up. Posts = sections + 1 to end the run + 1 per gate; runs that meet at a corner share the corner post, and a fence that closes on itself needs no end post.
• Rails: 2 per section for a fence up to 4 ft tall and 3 per section above that. Split rail defaults to 3-rail sections (our default; change it in the tool).
• Pickets = fence length in inches ÷ (actual board width + gap). The default 1/8 in privacy gap is the space ASTM F537 allows, as stated on the Home Depot cedar fence sheet. Board-on-board uses two layers, with the back boards spaced 4 in apart for 6 in boards. The 5% extra boards is our allowance for culls and cuts.
• Post holes default to 3× the nominal post width (12 in for a 4×4) and 1/3 of the above-ground height plus a 6 in gravel base (QUIKRETE's minimum). Concrete stops 3 in below grade, the post's own volume is subtracted, and 10% extra is added. Local frost-depth rules override these defaults.
• Bag yields match the concrete bag calculator: 0.30, 0.375, 0.45 and 0.60 cu ft for 40, 50, 60 and 80 lb bags. Fast-setting post mix lists the same 0.375 cu ft per 50 lb bag.
• Split rail: line posts about 10 ft 3 in apart, and if you use concrete, 12 in of compacted soil goes under it so the post bottom can drain (Culpeper). No drainage gravel is counted for split rail.
• Gate hardware, post caps, fasteners and stain are not counted.

Sources

1. Lowe's, Fencing Worksheet (How-To Guide). Posts = 1 per 6 or 8 ft section + 1 to end the run + 1 per gate; 2 backer rails per section for 4 ft fences, 3 for 6 ft; pickets = length in inches ÷ picket width (plus spacing). Worked example: 120 ft → 15 sections, 17 posts, 262 pickets.
2. The Home Depot, Cedar Fence Installation Suggestions. Three rails; 1/8 in between privacy boards per ASTM F537; board/batten privacy fence with bottom boards 4 in apart and top boards over the gaps.
3. Culpeper Wood Preservers, Split Rail Installation Instructions. Line posts about 10 ft 3 in apart; holes 24–30 in deep; if using concrete, 12 in of soil first and a concrete collar, never concrete under the post.
4. QUIKRETE, Setting Posts (project instructions). Hole 3× the post width, depth 1/3 to 1/2 of the above-ground post length plus 6 in, 6 in of gravel in the bottom, concrete to 3–4 in below ground level.
5. QUIKRETE, Fast-Setting Concrete Mix No. 1004 product data sheet. 50 lb bag ≈ 0.375 cu ft, 60 lb ≈ 0.45 cu ft; two 50 lb bags set a 3 in post in a 9 in hole 30 in deep.
6. QUIKRETE, Concrete Mix No. 1101 product data sheet. Bag yields: 40 lb ≈ 0.30 cu ft, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft.

Last reviewed October 25, 2026. Product figures vary by brand; the label on what you buy wins.