How the materials are worked out
The calculator splits each side into sections no wider than your post spacing and counts the posts from the sections. It counts pickets over the whole length at once, as UFP’s picket guide and Home Depot’s fence guide do, rather than section by section.
Worked example: 120 ft of 6 ft privacy fence
- Sections: 120 ÷ 8 = 15. Posts: 15 + 1 = 16 for one run with two free ends and no gate.
- Pickets: 120 ft is 1,440 in, and 1,440 ÷ 5½ in = 261.8, so 262 pickets of 1×6.
- Rails: 3 per section on a fence over 4 ft tall, so 45 rails, each a 2×4 8 ft long.
- Screws: 262 × 3 rails × 2 = 1,572 for the pickets, and 45 × 4 = 180 for the rails.
- Posts: 72 in of fence plus a 2 in gap is 74 in above the ground. Half of that, 37 in, goes in the ground, so each post is 111 in long: buy 10 ft posts.
- Holes: 3 × 3½ in = 10½ in across, and 37 + 6 = 43 in deep.
- Concrete: (π × 5¼² − 3½²) × 37 = 2,750.6 in³, or 1.59 ft³ a post. 16 posts take 25.5 ft³, which is 67.9 bags of 50 lb fast-setting mix at 0.375 ft³ each: buy 68.
- Gravel: π × 5¼² × 6 = 519.5 in³, or 0.3 ft³ a hole, so 4.8 ft³ for 16 holes.
UFP’s picket guide counts 120 ft with one gate the same way: 15 sections, 17 posts, 262 pickets and 17 post caps.
Posts, corners and gates
Home Depot and Lowe’s set fence posts 6 to 8 ft apart on center. Each side of the fence is split on its own, because a corner needs a post and it can’t fall in the middle of a section. UFP’s panel guide shows a fence with sides of 48, 24, 24, 16 and 8 ft: 6 + 3 + 3 + 2 + 1 = 15 sections. A side that doesn’t divide evenly gets one shorter section, so a 30 ft side with 8 ft spacing is three 8 ft sections and one of 6 ft.
A run with two free ends needs one post more than it has sections. A fence that closes on itself, all the way around a yard, needs one post per section, because the last section ends on the first post. Each gate adds a post: leave the opening out of the side lengths, and the fence gets another end there. Where a gate splits a side, enter the two parts as separate sides.
With prefabricated panels hung between the posts, set the spacing to the panel’s width plus one post’s width. Lowe’s vinyl fence guide sets end posts and gate posts 6 in deeper than the posts between them; the calculator gives every post the same depth.
Pickets: privacy, spaced and board-on-board
A 1×6 picket is 5½ in wide and a 1×4 is 3½ in. Privacy pickets touch, so each covers its own width. Spaced pickets each take their width plus the gap: Home Depot’s example of 5 in pickets with 3 in gaps along 120 ft is 1,440 ÷ 8 = 180 pickets.
On a board-on-board fence, Lowe’s overlaps each back picket 1 in onto the front pickets on each side. The front pickets then sit their width less 2 in apart, 3½ in for 1×6s, and a front and back pair repeats every 2 × 5½ − 2 = 9 in.
| Pickets for 120 ft | 1×6 (5½ in) | 1×4 (3½ in) |
|---|---|---|
| Privacy, touching | 262 | 412 |
| Spaced, 3 in gaps | 170 | 222 |
| Board-on-board, 1 in overlap | 320 | 576 |
Each count is 1,440 in divided by the space one picket takes (5½, 3½, 8½ or 6½ in), rounded up once for the whole fence. Board-on-board counts pairs: 1,440 ÷ 9 in = 160 pairs of 1×6s, and 1,440 ÷ 5 in = 288 pairs of 1×4s. None of the counts includes extra for culls or mistakes.
Rails and screws
Home Depot’s guide puts a top and a bottom rail on fences up to 4 ft tall and adds a third rail in the middle above that. Lowe’s uses one rail for every 2 ft of height, which is the same 3 rails at 6 ft but 4 at 8 ft. Pick the number of rails yourself to follow a different rule. The rails are 2×4s as long as the post spacing.
Home Depot calls for 2 or 3 fasteners where each picket crosses a rail; the calculator counts 2. It also counts 2 screws at each end of each rail, where the rail meets a post.
Post depth, holes and concrete
Home Depot and Quikrete both bury about a third of a post’s length, which is half of what stands above the ground. Home Depot’s example is an 8 ft post in a hole at least 2½ ft deep: a third of 96 in is 32 in. Trex Fencing says posts usually go at least 24 in deep, and its installation guide asks for 30 in on a 6 ft fence. The calculator takes the deepest of these and any frost depth you enter, then rounds the post up to an even number of feet.
Quikrete, Home Depot and Lowe’s all make the hole about three times the post’s width: 10½ in for a 4×4 and 16½ in for a 6×6. Gravel goes in the bottom for drainage, and the advice on how much varies: 3 to 4 in from Home Depot, 4 in from Lowe’s fence tips sheet, 6 in from Quikrete. The calculator uses Quikrete’s 6 in.
| One post | Depth | Hole | Concrete | 50 lb bags | 80 lb bags |
|---|---|---|---|---|---|
| 4 ft fence, 4×4 | 25 in | 10½ × 31 in | 1.08 ft³ | 2.87 | 1.79 |
| 6 ft fence, 4×4 | 37 in | 10½ × 43 in | 1.59 ft³ | 4.24 | 2.65 |
| 6 ft fence, 6×6 | 37 in | 16½ × 43 in | 3.93 ft³ | 10.48 | 6.55 |
| 8 ft fence, 4×4 | 49 in | 10½ × 55 in | 2.11 ft³ | 5.62 | 3.51 |
Each post stands 2 in taller than the fence. The concrete is the hole above the gravel, less the post itself. Bag yields are Quikrete’s: 0.375 ft³ for a 50 lb bag of Fast-Setting Concrete Mix, and 0.3, 0.45 and 0.6 ft³ for 40, 60 and 80 lb bags of Concrete Mix.
For a hole of your own size, or posts that aren’t part of a fence run, the post hole concrete calculator works out the bags for any hole and post. On sloping ground, the fence on a slope calculator works out how far each panel steps or racks and how tall each post stands.
Questions people ask
How many pickets do I need for 100 feet of fence?
For 1×6 pickets set side by side, 219. 100 ft is 1,200 in, and 1,200 ÷ 5½ in = 218.2, which rounds up to 219. With a 3 in gap each picket takes 8½ in, so 1,200 ÷ 8.5 = 141.2, or 142 pickets. A board-on-board fence of 1×6s repeats a front and a back picket every 9 in: 1,200 ÷ 9 = 133.3, so 134 pairs, or 268 pickets.
How many posts does a 100 ft fence need?
With posts no more than 8 ft apart, 100 ft splits into 13 sections (100 ÷ 8 = 12.5, rounded up). A straight run with two free ends needs one more post than it has sections: 14 posts. Add one post for each gate. A fence that closes on itself needs one post per section. If the fence turns corners, split each side on its own, because a corner post can’t sit in the middle of a section.
How deep should fence posts be?
About a third of the post’s length, which is half of what stands above the ground: Home Depot and Quikrete both give this rule. A 6 ft fence with a 2 in gap under it has posts standing 74 in, so they go 37 in deep and need to be 111 in long. Buy 10 ft posts. Home Depot’s example is an 8 ft post in a hole at least 2½ ft deep, and Trex Fencing’s installation guide asks for at least 30 in on a 6 ft fence. Enter a frost depth and the calculator sets the posts at least that deep.
How many bags of concrete does each fence post take?
A 4×4 on a 6 ft fence, in a 10½ in hole with 37 in of concrete over 6 in of gravel, takes about 1.59 ft³. That’s 4.24 bags of 50 lb fast-setting mix at 0.375 ft³ a bag, or 2.65 bags of 80 lb concrete mix at 0.6 ft³. Round up for the whole fence rather than post by post: 16 posts take 25.5 ft³, or 68 bags of 50 lb mix.
How many rails does a wood fence need?
Home Depot’s guide uses a top and a bottom rail on fences up to 4 ft tall and adds a third, middle rail above that. Lowe’s uses one rail for every 2 ft of height, which gives 4 rails on an 8 ft fence. Every section needs its own set: 120 ft in 8 ft sections takes 15 × 3 = 45 rails on a 6 ft fence.
How many screws do fence pickets need?
Home Depot says 2 or 3 fasteners where each picket crosses a rail. At 2 per rail, a picket on a fence with 3 rails takes 6, so 262 pickets need 1,572 screws. The calculator also counts 2 screws at each end of each rail: 180 for 45 rails.
Sources for the numbers on this page
- The Home Depot — How to build a fence (post spacing, hole depth, rails and pickets) · checked October 3, 2026
- Lowe’s — How to install a wood fence (post spacing and board-on-board overlap) · checked October 3, 2026
- Lowe’s — How to lay out and dig a post hole · checked October 3, 2026
- Lowe’s — Wood fence installation tips: installing posts and pickets (PDF) · checked October 3, 2026
- Lowe’s — How to install vinyl fencing · checked October 3, 2026
- UFP Industries — Fence picket installation guide, sold at Lowe’s (PDF) · checked October 3, 2026
- UFP Industries — How to install fence panels, sold at Lowe’s (PDF) · checked October 3, 2026
- Quikrete — Setting posts — project instructions · checked October 1, 2026
- Quikrete — Fast-Setting Concrete Mix No. 1004 — technical data sheet · checked October 1, 2026
- Quikrete — Concrete Mix No. 1101 — technical data sheet (bag yields, strength gain, curing) · checked October 1, 2026
- Trex Fencing — How deep should a fence post hole be? · checked October 3, 2026
- Southern Forest Products Association — Southern Pine standard sizes (nominal and actual dimensions) · checked October 3, 2026
Corrections and updates are logged on the sources page.