How many fence posts do I need?
Post count for the run, with the spacing adjusted so the last bay is not an odd one out.
The same page gives the hole depth for your frost line, the hole diameter for your post size and the concrete to fill it.
Worked example: 100 ft of 6 ft privacy fence
Eight-foot spacing is the conventional maximum for a 6 ft solid fence, and it is a maximum rather than a target. A 100 ft run does not divide by 8, so the fence is built at a slightly tighter spacing.
Why the spacing is a maximum, not a target
If you hold 8 ft spacing on a 100 ft run, the last bay is 4 ft and the second-to-last is 8 ft: an odd, weak-looking section at one end. Dividing the run into 13 equal bays of 7.69 ft spreads the difference across the whole fence.
The other half of the rule: never stretch a bay to reach a post. Posts set further apart than the fence system allows will lean within a season, and on a solid privacy fence the wind load makes it certain rather than likely.
Hole depth is set by frost, not by preference
A post hole that stops above the frost line will be pushed up by the ground freezing and thawing around it. That is the single most common reason a fence leans after two winters, and no amount of concrete compensates for it. The calculator takes the deeper of your post's minimum and your local frost depth.
These are starting points for planning, not code figures. Frost depth varies within a state, and your building department publishes the number that matters. In cold regions, setting the base of the hole below frost and widening the bottom into a bell shape resists heaving better than a straight cylinder, because the frozen soil grips the flared concrete.
Post spacing by fence type
| Fence type | Maximum spacing | Why |
|---|---|---|
| wood privacy (6 ft) | 8 ft | Six-foot privacy panels need a post every 8 ft or less; wind load on a solid fence is the limiting factor. |
| wood privacy (8 ft) | 6 ft | Taller panels catch more wind, so posts go closer: 6 ft is the usual maximum. |
| wood picket (4 ft) | 8 ft | An open picket fence lets wind through, so 8 ft spacing is normal. |
| chain link (4 ft) | 10 ft | Chain link is light and open; posts are set by the fabric roll length, usually 10 ft. |
| chain link (6 ft) | 8 ft | Taller chain link needs closer posts and heavier line posts. |
| vinyl privacy | 8 ft | Vinyl panels are manufactured to a fixed width, so spacing is set by the panel, not by choice. |
| composite privacy | 6 ft | Composite panels are heavier than vinyl; most systems specify 6 ft. |
| split rail (2 rail) | 10 ft | Rails come in 10 ft lengths, so posts are set at 10 ft. |
| split rail (3 rail) | 10 ft | Same as two-rail: the rail length sets the spacing. |
| decorative metal | 8 ft | Prefabricated panels arrive in 6 or 8 ft sections. |
| electric (livestock) | 15 ft | Temporary electric fencing uses widely spaced posts; permanent runs are closer. |