Setting 4 posts is not as easy as digging the holes and placing the post in the ground. If these posts represent the four corners of a structure, then they will need to be squared. Otherwise, the building materials that are attached to the posts will not fit properly. Over the years, the building industry has simplified the methods required for squaring four posts to include the do-it-yourself individual. This type of project can be completed in one to two days, depending on the size and scope of the job.
Set four 2-by-4 stakes in the ground to represent the four corner posts. Drive the first stake in the ground at the first corner. Pull a tape measure along the first wall out to the distance of the length of the wall. For example, if your four posts will be set 10 feet apart along the length and width of the building, then hook the tape measure to the first stake and pull it out 10 feet, placing a stake at 10 feet.
Calculate the distance from the first corner stake to a proposed stake that is diagonal to the first one and the third stake of the four corners. Use the triangulation method top figure the distance between the diagonals. Take the square of 10 feet and add them together and you have 200. Now take the square root of 200 to get the distance between the diagonals, which is 14.14 feet.
Pull the tape measure from the first stake at a diagonal of 14.14 feet and a separate tape measure from the second stake across at 10 feet. Align the two measurements, placing a stake in the ground where the 14.14 and 10-feet marks intersect. Now that you have three corners, repeat the process beginning with the second and third stakes to find the fourth corner. Place a stake at the fourth corner.
Paint a dot on the ground where each stake is driven, removing the stake first. Begin digging the post holes for the posts at the painted dots. This will ensure that all four posts are square.