Fence Replacement Calculator

150 ft of 6 ft privacy fence in one straight run with a 4 ft gate, posts every 8 ft, 3 rails per section, 5.5 in pickets, and 4×4 posts (3.5 in actual) set in 10.5 in holes 30 in deep with 6 in of gravel.

Fence:    150 − 4 ft gate = 146 ft, split by the gate into 2 segments
Sections: 146 ÷ 2 ÷ 8 = 9.125 → 10 per segment = 20
Posts:    (10 + 1) × 2 = 22, each 8 ft long
Rails:    20 × 3 = 60
Pickets:  146 × 12 ÷ 5.5 = 318.5 → 319
Concrete: 30 − 6 gravel − 3 top = 21 in deep
          (π × 5.25² − 3.5²) × 21 ÷ 1,728 = 0.903 cu ft per post
          ≈ 2.41 bags per post (not rounded)
Total:    0.903 × 22 posts = 19.88 cu ft
Bags:     19.88 ÷ 0.375 = 53 → 54 bags

segments       = straight runs + gates
sections       = (length − gate widths) ÷ segments ÷ spacing, rounded up, × segments
posts          = (sections per segment + 1) × segments
concrete depth = hole depth − gravel − 3 in left for soil
concrete/post  = (π × (hole ÷ 2)² − post²) × concrete depth ÷ 1,728   [cu in → cu ft]
bags           = concrete/post × posts ÷ bag yield, rounded up once

Each gate breaks the fence into separate segments with a post on each side, so gates add posts. The segments are assumed to be equal length; if your gate is near a corner the count can shift by a section. Bags are rounded once, on the total: a partly used bag at one hole finishes the next, so rounding each post separately would overbuy (it gave $66 bags for this example instead of $54).

Quikrete says two 50 lb bags set a 3 in square post in a 9 in hole 30 in deep. [1] Quikrete’s own method fills the hole to 3–4 in below the top and finishes with soil. With no gravel and a 4 in top gap, this formula gives about $2.19 bags for that hole ($2.28 with a 3 in gap), close to Quikrete’s 2. The remaining difference is that Quikrete’s figure is a rounded rule of thumb for dry-poured mix, and the bag yield itself is “approximately” 0.375 cu ft. Filled all the way to grade the same hole would take about $2.53 bags.

• Wind knocked down a few sections: set the length to just the damaged run, and set gates to 0 unless a gate is in it. Reuse sound posts if they are still solid.
• Pre-built panels: set picket width to 0. Sections equal the number of panels to buy.
• Backyard with three sides: enter the total length and set straight runs to 3 if the corners are not joined, or 1 if it is one continuous fence (corner posts are shared).
• 60 lb bags: change the bag yield to 0.45 cu ft, Quikrete’s figure for the 60 lb bag.

Concrete yield and hole-size rules come from Quikrete. Post spacing is an editable assumption, not a sourced figure. This page is quantity only: it uses no prices.

• [1] Quikrete — Fast-Setting Concrete Mix (No. 1004) data sheet, revised November 2025. Retrieved 2026-09-25. Quikrete Fast-Setting Concrete Mix: “Each 50 lb (22.6 kg) bag yields approximately 0.375 cu ft.” A 60 lb bag yields approximately 0.45 cu ft. Quikrete: “Two 50 lb (22.6 kg) bags … will set a 3 in (75 mm) square post in a 9 in (225 mm) diameter hole 30 in (0.75 m) deep.” Quikrete: “Start by digging the post hole about 3 times the diameter of the post.”
• [2] Quikrete — Setting Posts in Concrete. Retrieved 2026-09-25. Quikrete: dig the hole “three times the width of the post and at a depth equal to 1/3 to 1⁄2 of the above-ground length of the post, plus 6"”, then pour 6 in of gravel into the bottom.