Fence Calculator
Enter the run length and post spacing to get posts, sections, rails and pickets — plus the concrete needed to set every post, which is usually the item people underestimate.
How to use this calculator
- Measure the whole line first, including where gates will go, then enter the gate count and width. The tool subtracts the gate openings before working out sections, because a gate is not a fence section.
- Choose spacing before anything else. 8 ft is the common maximum for panel and picket fences; 6 ft is stronger, uses more posts, and is the better choice on windy sites or with heavy 6 ft privacy panels.
- Check the actual spacing in the result. The tool divides the run evenly, so if your line is 100 ft with 8 ft nominal spacing you get 13 sections at 7.7 ft — even, and better looking than twelve 8 ft bays and one 4 ft stub.
- Treat gate and corner posts separately. They carry the load. Set them deeper, in a wider hole, and use 6x6 if the design allows.
The formula
| Item | Calculation |
|---|---|
| Fence line | total length − (gates × gate width) |
| Sections | ceiling( fence line ÷ post spacing ) |
| Posts | sections + 1, plus one per gate |
| Rails | sections × rails per section |
| Pickets | ceiling( fence line in inches ÷ (picket width + gap) ) |
| Concrete per post | (hole volume − post volume) × 1.10 |
The post count catches people out: a fence needs one more post than it has sections, because both ends need one. On a 100 ft fence at 8 ft spacing that is 14 posts, not 13.
Hole volume is a cylinder: π × (diameter ÷ 2)² × depth. The post displaces its own square section, which is why a 4x4 in a 10 in hole needs less concrete than the hole volume suggests.
Worked example
100 ft of 6 ft privacy fence, 8 ft spacing, one 4 ft gate, 3 rails per section, 1x6 pickets butted tight, 4x4 posts in 10 in holes 30 in deep:
- Fence line: 100 − 4 = 96 ft
- Sections: 96 ÷ 8 = 12, actual spacing 8.0 ft
- Posts: 12 + 1 + 1 = 14
- Rails: 12 × 3 = 36 pieces, 288 linear ft
- Pickets: 96 × 12 ÷ 5.5 = 210
- Concrete per hole: (π × 0.417² × 2.5) − (0.292² × 2.5) = 1.15 cu ft, × 1.10 = 1.27 cu ft
- Total: 14 × 1.27 = 17.7 cu ft → 30 bags of 80 lb
Thirty bags is 2,400 lb of concrete for a fence people think of as a lumber project. It is usually the single heaviest item on the list.
Post spacing and depth
| Fence | Spacing | Post depth |
|---|---|---|
| 4 ft picket | 8 ft | 24 in |
| 6 ft privacy | 6–8 ft | 30 in |
| 6 ft privacy, windy site | 6 ft | 36 in |
| Ranch rail | 8–10 ft | 24–30 in |
| Gate and corner posts | — | 36–48 in, wider hole |
Frequently asked questions
How many posts do I need for a 100 ft fence?
At 8 foot spacing, 13 sections and 14 posts, because a fence needs one more post than it has sections. Add one more post per gate opening. At 6 foot spacing it is 17 sections and 18 posts.
How far apart should fence posts be?
Eight feet is the usual maximum for picket and panel fences, and six feet is better for 6 foot privacy fences or windy sites, since a tall solid fence acts as a sail. Panel fences are fixed by the panel width, normally 6 or 8 feet.
How much concrete per fence post?
For a 4x4 post in a 10 inch hole 30 inches deep, about 1.3 cubic feet — roughly two 80 lb bags. Multiply by your post count, and add extra for gate and corner posts, which should be set deeper in wider holes.
How many pickets do I need?
Divide the fence length in inches by the picket width plus the gap. For 96 feet of fence with 5.5 inch pickets butted tight, that is 1,152 divided by 5.5, or 210 pickets. Adding even a half inch gap drops it to 192.
Do gate posts need to be different?
Yes. A gate hangs its whole weight and every slam off one post, so gate posts should be larger, set deeper and in a wider hole than line posts — commonly a 6x6 at 36 to 48 inches deep even when the line posts are 4x4 at 30 inches.