Understanding your result
The headline is the number of posts, because posts set the layout and everything else hangs off them. The line beneath summarizes the rest of the order.
Sections between posts is the fence length, minus the gates, divided by your post spacing and rounded up. Because of the rounding, the real sections will be a little shorter than the spacing you entered. Post spacing if divided evenly gives the actual distance to mark out, so that every section is the same and you do not finish with one short bay at the end.
Post length to buy is the height of the fence plus the depth of the hole, rounded up to a length that lumber is sold in. A 6 foot fence with posts 3 feet in the ground needs 9 feet of post, so the calculator says to buy 10 foot posts and trim the tops.
Rails are counted at one length per section. Boards and pickets include 5% extra for splits and bad pieces. The fastener count assumes two screws or nails wherever a board crosses a rail.
How we calculate this
The hole is taken as about three times the width of the post: 10 inches across for a 4 × 4 and 16 inches for a 6 × 6. The post itself is subtracted from the volume of the hole, since concrete does not fill the space the post occupies.
The calculator treats the fence as one straight run. One end post is counted for the run, and one extra post for each gate, because a gate opening needs a post on both sides.
The assumptions behind the numbers
| Assumption | Value used | Why |
|---|---|---|
| Hole depth | Half the fence height, between 24 and 48 in | Puts one third of the post in the ground. Go deeper where frost requires it |
| Hole width | 10 in for 4 × 4 posts, 16 in for 6 × 6 | About three times the post width |
| Post size | Actual 3.5 in or 5.5 in square | Nominal sizes are larger than the real lumber |
| Rails | 2 up to 5 ft high, 3 above that | A middle rail keeps tall boards straight |
| Boards | 5% extra | Splits, knots and warped pieces |
| Fasteners | 2 per board at each rail | Standard practice for boards up to 6 in wide |
| Concrete bag | 50 lb fast-setting mix, 0.375 cu ft (20 kg in metric) | The usual product for setting posts |
| Layout | One straight run | Add a post for each corner that falls between post positions |
Assumptions last reviewed October 3, 2026.
The calculator does not check property lines, permits or height limits. Many towns and homeowner associations limit fence height and require the finished side to face outward. Call before you dig, too. In the US, dialing 811 gets buried utilities marked for free.
Two worked examples
A backyard privacy fence
A 6 foot privacy fence runs 150 feet, with one 4 foot gate. Posts are 4 × 4 at 8 foot spacing, and the boards are 5.5 inches wide, butted together.
- Fence to build: 150 − 4 = 146 ft
- Sections: 146 ÷ 8 = 18.25, so 19
- Even spacing: 146 ÷ 19 = 7.68 ft
- Posts: 19 + 1 + 1 = 21 posts, each 10 ft long
- Rails: 19 × 3 = 57 rails
- Boards: 146 × 12 ÷ 5.5 × 1.05 = 334.5, so 335 boards
- Fasteners: 335 × 3 × 2 = 2,010
- Concrete: 1.38 cu ft per hole × 21 = 29 cu ft, so 78 bags of 50 lb
Seventy-eight bags is almost two tons of concrete mix. That figure surprises most people, and it is the reason to price the concrete before settling on hole size. Dropping to a clean 8 inch hole, where the soil is firm enough to allow it, would cut it by more than a third.
A front-yard picket fence
A 4 foot picket fence runs 60 feet across the front of a lot, with a 3 foot gate. Posts are at 6 foot spacing. The pickets are 3.5 inches wide with 2.5 inch gaps.
- Fence to build: 60 − 3 = 57 ft
- Sections: 57 ÷ 6 = 9.5, so 10
- Even spacing: 57 ÷ 10 = 5.7 ft
- Posts: 10 + 1 + 1 = 12 posts, each 8 ft long
- Rails: 10 × 2 = 20 rails
- Pickets: 57 × 12 ÷ 6 × 1.05 = 119.7, so 120 pickets
- Fasteners: 120 × 2 × 2 = 480
- Concrete: 0.92 cu ft per hole × 12 = 11 cu ft, so 30 bags of 50 lb
The posts only need 6 feet of length, 4 above ground and 2 below. Lumber comes in 8 foot lengths, so each post is cut down, and the offcuts are long enough to use as bracing while the concrete sets.
Common mistakes
- Forgetting the gate posts. Every gate needs a post on each side. That is one more post per gate than the simple sum gives.
- Marking posts at the nominal spacing. If the run does not divide exactly, you end up with a short last section. Divide the run evenly instead.
- Buying posts the height of the fence. A third of the post goes in the ground. Buy for the full length.
- Setting posts too shallow. A 6 foot privacy fence is a sail. Two feet of post in the ground will not hold it in a storm.
- Counting boards by nominal width. A “1 × 6” fence board is 5.5 inches wide. Using 6 inches leaves you about 8% short.
- Using posts not rated for ground contact. Lumber treated only for above-ground use rots quickly once it is buried. Check the tag on the end of the post.
- Digging before calling. Have buried lines marked first. Fence post holes are exactly the depth of many service lines.
Printable shopping list
Print shopping list produces a full order on one page: posts with their length, rails, boards or panels, fasteners, concrete, and gate hardware. Take the even-spacing figure with you as well, on the breakdown table. That is the measurement you will mark on the string line before digging the first hole.
Questions people ask
- How many fence posts do I need?
- Divide the fence length by the post spacing, round up, and add one. A straight 96 foot run with posts every 8 feet has 12 sections and 13 posts. Each gate adds one more post, and so does any corner that does not land on a post position.
- How far apart should fence posts be?
- Between 6 and 8 feet for most wood fences. Eight feet suits standard rails and ready-made panels. Closer spacing, around 6 feet, makes a stronger fence and is a good idea for tall privacy fences in windy places.
- How deep should fence posts be set?
- A common rule is to bury a third of the post's total length, which works out to half the height of the fence above ground. A 6 foot fence gets a 3 foot hole, and a 4 foot fence a 2 foot hole. Where the ground freezes, the bottom of the hole should also be below the frost line.
- How many pickets do I need per foot of fence?
- Divide 12 by the picket width plus the gap, in inches. For 5.5 inch boards with no gap, that is about 2.2 boards per foot. For 3.5 inch pickets with a 2.5 inch gap, it is exactly 2 per foot.
- How much concrete does each fence post need?
- For a 4 × 4 post in a 10 inch hole, about 0.9 cubic feet in a 2 foot hole and about 1.4 cubic feet in a 3 foot hole. That is roughly three to four 50 pound bags of fast-setting mix per post.
- How many rails does a fence need?
- Two rails for fences up to about 5 feet, and three rails for 6 foot fences. The third rail in the middle stops tall boards from warping and cupping between the top and bottom.
Built and reviewed by Bertha
Last updated · How we work out our numbers