Fence Calculator
Estimates only. Check your local frost depth, permit and height rules, and the yield printed on your concrete bag before digging.
A 100 ft fence with posts 8 ft apart needs 13 sections and 14 posts, plus up to one more section for every corner and gate. Each 4×4 post set in a 10½-inch hole 30 inches deep, on 6 inches of gravel, takes about 1.1 cubic feet of concrete, or three 50 lb bags. Enter your fence line, height, and post spacing below for posts, pickets or panels, rails, concrete, and cost per foot.
Concrete per fence post by post and hole size
| Post | Round hole (width × depth) | Concrete per post | 50 lb bags | 80 lb bags |
|---|---|---|---|---|
| 4×4 (3½") | 10" × 24" | 0.69 ft³ | 1.8 | 1.2 |
| 4×4 (3½") | 10½" × 30" | 1.03 ft³ | 2.8 | 1.7 |
| 4×4 (3½") | 12" × 36" | 1.75 ft³ | 4.7 | 2.9 |
| 5×5 vinyl | 15" × 30" | 2.11 ft³ | 5.6 | 3.5 |
| 6×6 (5½") | 16½" × 30" | 2.55 ft³ | 6.8 | 4.2 |
| 6×6 (5½") | 16½" × 42" | 3.82 ft³ | 10.2 | 6.4 |
How to calculate fence posts
A straight fence is a row of sections with a post at each end. Divide the fence length by the post spacing and round up to get the sections, then add one post: posts = sections + 1. A 100 ft run with posts 8 ft apart is 12.5 sections, rounded up to 13, so it needs 14 posts.
Corners and gates are where hand counts go wrong. Every corner splits the fence into two runs that each round up on their own, so a corner can add a section. Every gate interrupts a run and needs a sturdy post on both sides of the opening. The calculator adds a section for each corner and gate, a shared post at each corner, and an extra post for each gate. That can come out one post high on a closed loop or a gate at the end of a run, but it is never short. Enter the full fence line including the gates; the gate openings are subtracted before sections are counted.
How far apart fence posts should be
Most residential privacy fences set posts 6 to 8 feet apart, according to Decks.com's spacing guide. 8 feet is the standard because it lets you use stock 8 ft 2×4s for the rails, and 6 feet holds up better in strong wind. Vinyl fences often run 8 to 10 feet and chain link 10 to 12, but prefab panels fix the spacing for you, so use the on-center figure from the panel's install guide.
Pickets, rails, and panels
Pickets are counted along the whole fence line, gates included, since gate leaves are usually clad with the same boards: pickets = fence length ÷ (picket width + gap). Use the actual width, not the nominal size. A 1×6 picket is 5½ inches wide, so a solid 100 ft privacy fence takes 1,200 ÷ 5.5 = 219 pickets. For board-on-board, pickets alternate front and back and overlap, so the count is fence length ÷ (width − overlap): 267 boards for the same fence with a 1-inch overlap. Rails are counted per section; the presets use two for a 4 ft picket fence and three for a 6 ft privacy fence. Panel fences need one panel per section and no separate rails or pickets.
Worked example: a 100 ft wood privacy fence
A straight 100 ft fence, 6 feet tall, with 4×4 posts 8 feet apart needs 13 sections, 14 posts, and 39 rails. With 5½-inch pickets and 5% extra, that is 230 pickets. Each post goes in a 10½-inch hole 30 inches deep with 6 inches of gravel, so 24 inches of concrete surrounds the post. That is 1.14 cubic feet per post with 10% extra for irregular holes, or 43 bags of 50 lb concrete for the whole fence (27 bags of 80 lb). The gravel takes 9 bags of 50 lb, and each post should be 8 feet long: 6 feet above ground and 2 feet in concrete.
How much concrete per fence post
QUIKRETE's post-setting guide sizes the hole from the post: make it three times as wide as the post and one-third to one-half of the post's above-ground height deep, plus 6 inches for a gravel base. A 6 ft fence with 4×4 posts gets a hole about 10½ inches across and 30 to 42 inches deep. The gravel lets water drain away from the end grain, and the concrete is finished sloping away from the post so rain runs off. Where the ground freezes, the bottom of the hole also needs to sit below the local frost line, which your building department can give you.
The concrete fills the hole above the gravel, minus the space the post takes up: concrete per post = (hole area − post area) × (hole depth − gravel). The calculator adds 10% by default because dug holes are never perfectly round or square, then divides by the yield of your bag size using QUIKRETE's published yields: 0.30 cubic feet for a 40 lb bag, 0.375 for 50 lb, 0.45 for 60 lb, and 0.60 for 80 lb. The table above shows how fast the number climbs with post and hole size. The common "two bags per post" shortcut only holds for small holes; a 6×6 gate post in a deep hole can take ten 50 lb bags.
Fast-setting or regular concrete
Fast-setting post mix is poured into the hole dry around the braced post and then soaked with water, with no mixing, which is why it is the usual choice for fences. Regular concrete mix is mixed first and takes longer to set, but costs less per bag. Both are counted the same way: check the yield printed on your bag and pick the matching size above.
Fence cost per foot
Enter prices for posts, pickets or panels, rails, and concrete, and the calculator totals your materials and divides by the fence length for a cost per foot. That is the DIY figure. Installed prices add labor, which Inch Calculator puts at about $5 to $15 per linear foot.
| Fence | Installed, per foot |
|---|---|
| Chain link | $5–$15 |
| Wood picket, 4 ft | $10–$36 |
| Wood privacy, 6 ft | $13–$45 |
| Vinyl picket, 4 ft | $15–$35 |
| Aluminum | $20–$55 |
| Vinyl privacy, 6 ft | $30–$55 |
Fence types
- Wood privacy fence. Solid boards edge to edge on three rails, usually 6 feet tall. The default preset. Pressure-treated or cedar pickets shrink as they dry, which opens small gaps between boards.
- Board-on-board. The fix for those gaps: boards alternate front and back with an overlap, so it stays solid as the wood moves. It takes about 20% more boards than a side-by-side privacy fence.
- Picket fence. Shorter and open, with narrower pickets spaced apart on two rails. Set the gap to the spacing you want; the count changes fast with it.
- Vinyl and prefab panels. Sold as finished sections, so you count panels and posts rather than pickets and rails. Vinyl posts are often 5×5 inches and slip over or are set in concrete according to the manufacturer.
- Chain link and metal. These use different parts (line posts, terminal posts, top rail, and mesh rolls) that this calculator does not list. You can still use the Prefab panels option with your post spacing to count the posts and the concrete to set them.
Common mistakes
- Dividing length by spacing and stopping. 100 ÷ 8 gives 12.5, not the 14 posts you need. Round the sections up, add one post, then add for corners and gates.
- Using nominal board sizes. A 1×6 picket is 5½ inches wide and a 4×4 post is 3½ inches. Counting with 6 and 4 leaves you short of pickets and overestimates the post in the hole.
- Skipping the gravel. Concrete poured straight onto soil traps water against the bottom of the post, where wood posts rot first. Six inches of gravel lets it drain.
- Holes that are too shallow. A post set less than a third of its above-ground height deep leans in wind, and above the frost line it can heave in winter.
- Buying posts too short. A 6 ft fence with 2 feet in the ground needs 8 ft posts, not 6 ft ones. The calculator shows the length to buy.
What this calculator can't handle
- Slopes. On a hill, a racked fence follows the grade and a stepped fence drops in level sections. Measure along the ground for the length and expect longer posts on stepped fences.
- Curved fence lines. Measure the length along the curve and use closer post spacing; the section count will be close, but plan extra pickets for the cuts.
- Gates. The calculator places the gate posts and the concrete for them, but not the gate frame, hinges, or latch. Gate posts carry the most load, so many builders use a bigger post and a deeper hole there.
- Rock, roots, and utilities. Call 811 before you dig. Buried lines and rock change where the posts can go.
- Local rules. Height limits, setbacks, and permit requirements vary by town and HOA. Check them before you order materials.
About these figures: hole width, depth, and the gravel base follow QUIKRETE's guide to setting posts in concrete, and bag yields are QUIKRETE's published figures. Post spacing follows Decks.com's fence post spacing guide, and installed costs per foot come from Inch Calculator's fence cost guide. The rail counts in the presets are common practice, not a published standard, so adjust them to your design. Gravel weight uses the same density as our gravel calculator.
Frequently asked questions
How many fence posts do I need?
Divide the fence length by the post spacing, round up to whole sections, and add one post. A 100 ft fence with posts 8 ft apart needs 13 sections and 14 posts. Add a post for each gate, and allow an extra section for each corner and gate, since each separate run rounds up on its own.
How many bags of concrete do I need per fence post?
A 4×4 post in a 10½-inch hole 30 inches deep, on 6 inches of gravel, takes about 1 cubic foot of concrete: three 50 lb bags or two 80 lb bags. Bigger posts and deeper holes take much more. A 6×6 post in a 16½-inch hole 42 inches deep needs about ten 50 lb bags. Enter your post and hole size for the exact count.
How deep should fence posts be?
Dig one-third to one-half of the post's above-ground height, plus 6 inches for gravel, according to QUIKRETE. For a 6 ft fence that is 30 to 42 inches. Where the ground freezes, the hole should also reach below the local frost line so the post doesn't heave in winter.
How far apart should fence posts be?
Set wood privacy fence posts 6 to 8 feet apart, on center. 8 feet suits standard 8 ft rails, and 6 feet is stronger in wind. Vinyl fences often allow 8 to 10 feet and chain link 10 to 12, but prefab panels set the spacing, so follow the panel's install guide.
How wide should a fence post hole be?
Make the hole about three times the width of the post. A 4×4 post (3½ inches actual) needs a hole about 10½ inches across, so a 10- or 12-inch auger works. A 6×6 post (5½ inches) needs about 16½ inches.
How many pickets do I need for a 100 ft fence?
A solid privacy fence of 1×6 pickets (5½ inches actual) takes 219 pickets per 100 feet, or about 230 with 5% extra for splits and cuts. Board-on-board with a 1-inch overlap takes about 267. Spaced pickets need fewer: 1×4 pickets (3½ inches) with a 2½-inch gap take 200 per 100 feet.
How many rails does a fence need?
Most builders use two rails per section on fences up to about 4 feet and three rails on 5 to 6 ft privacy fences, so the boards don't bow between rails. Multiply the rails per section by the number of sections. A 100 ft fence with 13 sections and three rails needs 39 rails.
Do I need gravel under a fence post?
Yes. QUIKRETE recommends 6 inches of gravel in the bottom of the hole so water drains away from the post instead of pooling against the end grain. The post sits on the gravel and the concrete fills around it above that layer.
How long should fence posts be?
Add the fence height to the depth set in concrete. A 6 ft fence with 24 inches of concrete above the gravel needs 8 ft posts. A 4 ft fence with posts set about 16 inches deep can use 6 ft posts.
How much does a fence cost per foot?
Installed prices run about $5 to $15 per foot for chain link, $13 to $45 for a 6 ft wood privacy fence, and $30 to $55 for 6 ft vinyl privacy, according to Inch Calculator's cost guide. Labor is about $5 to $15 of that per foot. Enter your material prices in the calculator for your own materials cost per foot.
Related calculators
Sources
- Setting Posts in ConcreteQUIKRETEHole three times the width of the post, 1/3 to 1/2 of the above-ground post length deep plus 6 in., 6 in. of gravel in the bottom, and the concrete finished sloping away from the post.
- Concrete Mix No. 1101 — Product Data and YieldQUIKRETEBag yields used for the concrete count: 0.30 ft³ (40 lb), 0.375 ft³ (50 lb), 0.45 ft³ (60 lb), and 0.60 ft³ (80 lb).
- Fence Post Spacing: How Far Apart Should Fence Posts Be?Decks.com (Trex)Residential privacy fence posts 6–8 ft apart, vinyl 8–10 ft, chain link 10–12 ft, and hole depth of 1/3 to 1/2 of the above-ground post height.
- Cost to Install a FenceInch CalculatorInstalled cost per linear foot by fence type (chain link $5–$15, 6 ft wood privacy $13–$45, 6 ft vinyl privacy $30–$55) and labor of about $5–$15 per foot. Updated July 2023.