The depth of your post holes is the most important factor in the stability of your fence. If you do not get the post holes deep enough, there is a greater potential that your fence can be blown over. There are different opinions on just how deep the post holes should be. Another important factor to consider when digging post holes is knowing where cable lines and gas lines are located. These lines are typically run underground, and they can easily be cut with a shovel or an auger. Before ever digging your fence post holes, call your cable company and gas company. The cable and gas companies will come to your home and mark exactly where the lines are located with flags and spray paint. This will help you to avoid interrupting services or potentially putting yourself in danger.
Post lengths for fences start at 2.4 m (8 feet) long; they start at 10 cm by 10 cm (4 inches by 4 inches) in diameter. Posts can also be purchased in greater lengths for digging deeper holes. The average height of a fence panel is 1.8 m (6 feet), and the average length of each fence panel is 2.4 m (8 feet). Post holes can be dug with a shovel, or you can use an auger. An auger is a drill like machine that is more easily capable of digging out post holes in hard ground.
The width of your post holes should be at least a minimum of 25 cm (10 inches) wide. This width will allow adequate room for concrete to be poured into the holes. Not all fence installers use concrete to set the posts, but the vast majority do. Concrete provides the most strength for your posts. There are some fence builders that will refill the holes with the dirt that was removed from digging, and with rock. This procedure does make it easier to replace a post if it should happen to break or split.
Panel post depth
The minimum depth that you should dig your fence post holes is 60 cm (2 feet). The maximum depth that you should consider digging the post holes is 90 cm (3 feet) deep. The deeper you dig the holes, the more stability your fence has, but you must also purchase longer posts. You will also need to trim off 30 cm (1 foot) in length to accommodate the height of the fence panels.
Post hole depth for gates
The minimum depth for your gate posts is considered to be 80 cm (32 inches). The reason for this depth is that the posts must be able to handle the weight and the movement of the gate. Concrete must also be poured into the post holes. The movement of the gate will loosen your posts -- and cause them to lean or eventually break -- if you do not concrete them in place.
Your concrete should be a gravel mix. It can be purchased at the same place you purchase your fence posts. Your supplies are usually bought at your local home remodelling store. Concrete for fence posts typically comes in 18 and 27 kg (40 and 60 lb) bags. For fence post holes that are 60 cm (2 feet) deep use at least one 18 kg (40 lb) bag of concrete. For post holes that are 80 cm (32 inches) deep to 90 cm (36 inche)s deep, use a 27 kg (60 lb) bag of concrete.