How the fence calculator works
The concrete figure assumes 4×4 posts (3.5 inches square). Many builders put a few inches of gravel in the bottom of each hole for drainage — that slightly reduces the concrete you need.
How deep should fence posts be?
A common rule is to bury about one third of the post's total length — about 2 ft for a 6 ft fence on an 8 ft post — and to go below the frost line in cold climates. Your local building department can tell you the required depth and whether a permit is needed.
Post hole size
Holes are usually about three times the post width: roughly 10–12 inches across for a 4×4 post. Wider holes use more concrete without adding much strength.
Before you dig
- Call 811 a few days before digging so buried utility lines can be marked — it's free.
- Confirm your property line and any HOA rules on height and style.
- Set the corner and end posts first, run a string line, then fill in the line posts.
Frequently asked questions
How many fence posts do I need for 100 feet?
With 8 ft spacing, 14 posts (13 sections). With 6 ft spacing, 18 posts.
How many bags of concrete per fence post?
For a 10-inch hole 24 inches deep around a 4×4 post, about 2.5 bags of 50 lb fast-setting concrete, or 1.5 bags of 80 lb mix.
How many pickets for a 6 ft privacy fence?
With 5.5-inch pickets and no gaps, about 2.2 pickets per foot of fence — roughly 219 pickets per 100 ft.