Reference
Fence post spacing and post sizes
Every common fence type, its maximum span, and why the limit exists.
Spacing by fence type
| Fence type | Maximum | Reason for the limit |
|---|---|---|
| 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. |
Post sizes and hole dimensions
| Post | Actual width | Hole diameter | Minimum depth | Use |
|---|---|---|---|---|
| 4x4 (3.5 in actual) | 3.5 in | 9 in | 24 in | Light picket and lower chain link. |
| 4x6 (3.5 x 5.5 in) | 5.5 in | 10 in | 30 in | Rail and gate posts for a low fence. |
| 6x6 (5.5 in actual) | 5.5 in | 12 in | 30 in | The standard for privacy fencing and for gate posts. |
| round post (4 in) | 4 in | 9 in | 24 in | Steel or treated round posts. |
| round post (5 in) | 5 in | 10 in | 30 in | Heavier round posts and corners. |
Minimum depth is the shallowest that is normally acceptable; the frost line overrides it wherever frost reaches deeper.
Frost depth by region
Planning figures only. Frost depth varies within a region and your building department publishes the number that governs.
The rule behind all of it
Post spacing is limited by how much load the post has to carry and how much the fence can flex between supports. An open fence sheds wind, so it can span further. A solid fence acts as a sail, so its posts go closer and its holes go deeper.
Post depth follows a different rule: it is about frost, not load. A shallow hole in a freezing climate will lift regardless of how much concrete is in it. If your frost depth is 42 in, your holes are 42 in deep whatever the fence type.
Locating buried services
Before any digging, have buried lines marked. In the United States the free service is 811; call or submit a request a few days before you plan to dig. Damaging a gas, water or fibre line is expensive, dangerous, and in most places your responsibility. In the UK the equivalent is a line search through your utility providers.
Corners, ends and gates
A corner post is braced in two directions and a gate post carries a moving load, so both should be set deeper and in more concrete than a line post. A common approach is one post size up and 6 in deeper for gate posts: on a 6 ft fence, that means a 6x6 set 36 in deep with a wider hole rather than a 4x4. Gates sag because their posts move, almost always within the first year.