A fence estimate starts with posts. Once you know how many sections the fence breaks into, the rails, pickets and concrete follow from simple multiplication. This calculator works out sections from the fence length and post spacing, adds posts for corners and gates, counts rails and pickets, and sizes the concrete for every post hole, so you can price a privacy or picket fence before you dig.
How to use the fence calculator
- Choose US or Metric units.
- Enter the total fence length, including gates, and the fence height.
- Enter the maximum post spacing — 8 ft is standard for wood.
- Enter the number of corners and gates and the gate width.
- Set the rails per section and the picket width and gap.
- Choose the post type and the hole diameter and depth for the concrete estimate.
Fence formulas
Concrete per hole is the volume of the hole, π × (diameter ÷ 2)² × depth, minus the part of the post inside it. Each corner is treated as adding a short section, which is usually what happens when runs are not exact multiples of the spacing.
Worked example: a 150 ft privacy fence
Fence without the 4 ft gate: 146 ft. Sections: ⌈ 146 ÷ 8 ⌉ + 2 corners = 21.
Posts: 21 + 1 + 1 gate = 23 posts, each 8 ft (6 ft above ground, 24 in buried). Rails: 21 × 3 = 63.
Pickets: 1,800 in ÷ 5.5 in = 327.3; with 5% extra → 344 pickets.
Concrete: a 10 in hole 24 in deep around a 4×4 holds 0.92 ft³, so 23 posts need 21.2 ft³ — about 36 bags of 80 lb.
Typical fence specifications
| Item | Common choice |
|---|---|
| Post spacing | 8 ft on center (6 ft for heavy or windy sites) |
| Posts | 4×4 for most fences; 6×6 or steel at gates and tall fences |
| Rails | 2 for up to 4 ft; 3 for 5–6 ft; 4 for 8 ft |
| Pickets | 1×4 or 1×6, butted for privacy, gapped for picket style |
| Hole diameter | About 3× the post width |
| Hole depth | ⅓ of the post length, at least 2 ft, below frost depth |
Pickets on a privacy fence usually stop about 2 inches above the ground so they do not wick moisture. Gate posts take more strain than line posts, so many builders use larger posts, deeper holes or a diagonal brace on the gate frame.
Before you build
- Call 811 a few days before digging so utility lines are marked. The service is free, and most states require a call before any digging.
- Confirm the property line. A survey or recorded plat avoids building on a neighbor’s land.
- Check local rules. Many towns limit backyard fences to 6 ft and front-yard fences to 3 or 4 ft, and homeowners associations often control style and color.
- Face the good side out where local ordinances require it.
Bagged concrete is fine for a few dozen holes; for larger jobs, compare the concrete calculator results against a short-load delivery. If you are setting posts in gravel instead, the gravel calculator converts the hole volume into tons. Building a deck at the same time? The deck calculator handles boards, joists and screws.
Frequently asked questions
How many fence posts do I need for 100 feet?
For a straight 100-foot run with posts every 8 feet, divide 100 by 8 and round up to 13 sections, then add one: 14 posts. Each corner and each gate typically adds one more post, because they force a section to end early.
How deep should fence posts be set?
A common rule is to bury about one-third of the post's total length and never less than 2 feet, so a 6-foot fence uses 8-foot posts set 2 feet deep. Where the ground freezes, go below the local frost depth to stop frost heave, and set gate posts deeper.
How many pickets are in an 8-foot fence section?
Divide the section length by the picket width plus the gap. With 5½-inch pickets butted together, 96 inches takes 17.5, so 18 pickets. With 2-inch gaps, the same section takes 96 ÷ 7½ = 12.8, so 13.
How many bags of concrete per fence post?
It depends on the hole. A 4 × 4 post in a 10-inch hole 24 inches deep needs about 0.92 cubic feet of concrete, roughly one and a half 80-lb bags or two and a half 50-lb bags of fast-setting mix.
Do fence posts have to be set in concrete?
Not always. Concrete is the most common choice and resists wind and sagging gates well. Some builders set wood posts in tamped gravel, which drains better and makes posts easier to replace. Either way, a few inches of gravel at the bottom of the hole helps water drain away from the post end.