Fence posts should be installed to coincide with the purpose and durability desired of the fence. A temporary fence to discourage people from going through a building site will not need to be as strong as a permanent fence to keep livestock in check. The type of post installed will also help to determine the distance between set posts. Wood and steel posts require less distance than a temporary electric fence that uses rods and insulators to carry the wire.
Permanent barbed wire fences
The exterior perimeter of a pasture to hold livestock such as cattle and horses needs to be a minimum of 1.2 m (4 feet) high and have a lifespan of more than 20 years. The maximum distance between wood or metal T-post should be 5 m (16.5 feet). The recommended distance is 3.6 m (12 feet). This adds strength and extra support to the fence line. Wooden fence posts should extend a minimum of 10 cm (4 inches) above the top wire of the fence. This is to prevent splitting of the wood when attaching the wire to the post. Posts should be buried a minimum of 45 cm (18 inches) unless the danger of perma-heave from ground freeze/thaw would uproot the posts. Under those circumstances, a depth of 90 cm (3 feet) burial of a fence post is recommended.
Electric fences can be installed for temporary control of livestock. A good example is to put up a temporary electric fence around a winter forage crop. Normally, a temporary fence is expected to last a few months or a single season. A 90 cm (3 foot) tall rebar will adequately contain animals that have been previously exposed to hot or electrified fence wires. The rebar can be inserted into the ground approximately 30 cm (1 foot) deep, and one post is needed for every 15 m (50 feet). More posts can be used if necessary to keep the electric or hot wire off the ground.
Factors about terrain
Consider the terrain of your fence line. If your fence passes over steep hills or is in a location of high erosion, you will probably want to use additional fence posts to your fence line.