Fence Calculator: Posts, Pickets, Panels

Why our numbers are more realistic

One fence calculator we reviewed gives a flat "about 2 bags of concrete per post." We work the concrete out from the hole itself. Here's what changes:

Typical calculator	This calculator	Why it matters
One calculator we reviewed gives about 2 bags (60 lb) of concrete per post	Concrete calculated from your hole size and depth, with the post's own volume subtracted	Quikrete's own example, 2 bags, is for a 4 in post in a 10 in hole 2 ft deep, with the last few inches filled with soil. A 4x4 buried 3 ft in a 12 in hole needs about 1.9 cu ft of concrete when you stop 3 in short and top it with soil, or 2.1 cu ft filled to ground level, with the gravel below. That's 4 to 5 bags of 60 lb.
A fixed hole depth, or one that ignores frost	Half the above-ground height buried, at least 24 in, and at least your frost depth plus 6 in if you enter it	A taller fence catches more wind, so it needs a deeper post, and a post set above the frost line can heave when the ground freezes.
Gate and corner posts treated like any other post, or left out	Counted separately and set 6 in deeper	A fence maker's install sheet sets end, corner, and gate posts at least 6 in deeper than line posts. Count them as line posts and you come up short on post length and concrete.
Many fence calculators count concrete for every post, with no gravel option	Your pick: concrete, a concrete collar over packed gravel, packed gravel only, or gravel for line posts with concrete for corner, gate and end posts, with the gravel counted in 0.5 cu ft bags	Setting a post in gravel is a different shopping list, not a smaller one. A 4x4 buried 36 in, in a 12 in hole with 4 in of gravel under it, takes about 2.8 cu ft of tamped gravel, about 6 bags, and no concrete.
Some calculators don't take gate openings out of the pickets or handle board-on-board	Pickets from board width and gap, doubled for board-on-board, with gate openings taken out	The gap changes the count a lot: 100 ft of fence takes 219 boards of 5.5 in laid tight, but only 150 with 2.5 in gaps. Board-on-board takes twice as many, and a 4 ft gate opening needs about 9 fewer fence boards.

How this works

Posts = sections + 1 + 1 per gate. Sections = (run minus gate openings) ÷ post spacing, rounded up, plus one per corner and one per gate, a planning allowance because the runs on each side rarely divide evenly. Concrete per hole = (hole area − post area) × concrete depth, which is the buried depth, less 3 in if you top the hole with soil. Gravel sits below that, so hole depth = buried depth + gravel, and post length = height + buried depth. Bags = total volume plus 10% for spillage and uneven holes, ÷ bag yield, rounded up once for the whole fence. Gravel is counted in 0.5 cu ft bags. Rails = rails per section × sections. Pickets = fence length × 12 ÷ (picket width + gap), rounded up.

Post depth: half the above-ground height is buried, which is a third of the post (36 in for a 6 ft fence). Never less than 24 in, and at least 6 in below your frost depth if you enter one. Corner, gate, and end posts go 6 in deeper.
Hole width: 3 times the post width, rounded up to an even inch (12 in for a 4x4).
Bag yield: 0.375 cu ft for a 50 lb bag of fast-setting mix, and 0.45 for 60 lb and 0.60 for 80 lb of regular concrete mix, from the bag maker's data sheets.
Top of the hole: Quikrete's setting-posts steps stop the concrete 3 to 4 in below ground level and finish with soil; we use 3 in, about 8% less concrete on a 36 in post (3 in of 36). Others fill to ground level and slope the top so water runs off. Both are common, so you pick.
Setting the posts: "In concrete" is the method above. "Concrete collar" packs gravel around the lower third of the post's depth and fills the top two-thirds with concrete. "Packed gravel only" fills the hole with crushed gravel tamped up to ground level. The last choice sets line posts that way and corner, gate and end posts in concrete. Gravel around a post is the hole minus the post, plus 20% because loose stone packs down when it's tamped. Highway figures show compacted crushed stone weighing 25 to 30% more than loose; hand tamping packs less, so we use 20%, as our gravel calculator does for crusher run.
Pre-built panels: the posts go one panel width apart, and each section takes one panel, so panels = sections, corner and gate allowance included. No rails or pickets are counted.
Rails per section: 2 up to 4 ft tall, 3 above that up to 6 ft, 4 above 6 ft. Three on a 6 ft panel comes from a manufacturer's kit; the other two are trade rules.
Waste: 10% on rails and pickets, a trade figure.
Big jobs: from about 1 cubic yard of concrete we show the weight of the bags, and from 2 cubic yards we suggest pricing ready-mix or a mixer rental, as our concrete calculator does.
Our concrete calculator uses the same hole method and the same 10% allowance, so the concrete per hole matches. Use it for a single post, a deck or a mailbox.
Corner, gate, and end posts: two ends, every corner, and both sides of each gate. A gate at an end or corner shares a post, so the count can include one hole 6 in deeper than needed, less than a bag.

Common questions

How many bags of concrete per fence post?

For a 4x4 on a 6 ft fence, about 3½ bags of 80 lb (4 to 5 of 60 lb), not the 2 you often see quoted. The post goes 36 in into a 12 in hole, and filling that around the post takes about 1.9 cu ft of concrete if you stop 3 in short and top it with soil, or 2.1 cu ft to ground level. Add 10% for spillage. Corner, gate and end posts go 6 in deeper and take a little more, and frost depth can add a lot.

Can I set fence posts in gravel instead of concrete?

Yes, for plain line posts in firm soil that drains. University guidance recommends packed crushed rock, because water drains away from the post instead of sitting against it. Use crushed gravel with mixed sizes, not round pea gravel, and tamp it in layers of 4 to 5 in. Gate, corner and end posts take the most strain, so setting guides put gate and corner posts in concrete, end posts carry the same pull, and concrete is also the better pick in loose or sandy soil. Pick "Gravel for line posts, concrete for corner, gate and end posts" above to count both.

How far apart should fence posts be?

8 ft is common for wood fences. For pre-built panels, the panel sets it: pick "Pre-built panels" and their width, and the posts follow.

What this doesn't cover

Fasteners. The count depends on your boards and fasteners, so go by the box.
Gate frames, gate pickets, hinges, latches, and post caps.
Metal and chain-link fences, and decks. For vinyl panels the panel count works, but use the post and hole sizes on the maker's sheet.
Permits, setbacks, and property lines. Before you dig, call 811 (free; most states require it) so buried lines get marked.

Sources

Quikrete fast-setting concrete mix data sheet: hole depth one-half of post height, hole three times the post width, 0.375 cu ft per 50 lb bag.
Quikrete, setting posts: gravel at the bottom of the hole, concrete stopped 3 to 4 in short and topped with soil.
Ask Extension, setting fence posts: half the above-ground height buried, and packed crushed rock drains better than concrete.
Long Fence, how deep to dig fence posts: a third to a half of the post, at least 6 in below the frost line.
UFP Outdoor Essentials fence install sheet: 6 ft panels, 3 rails, 6 in gravel, end, corner, and gate posts 6 in deeper.
Ask the Builder, fence posts: crushed gravel tamped in 5 in layers for line posts, concrete at corners and gates.
Fine Homebuilding forum, setting fence posts: builders' experience with gravel lifts of 4 to 5 in and gravel-and-concrete collars.
Invoicer fence calculator: the "about 2 bags per post" figure and the rail counts by height we compare against.

Numbers last reviewed: October 9, 2026.