Once the string line is up, you can start to lay out the posts. Typical post spacing is 8 feet on center for wood rail and/or board fences and 12-14 feet on center for field fence or barbed/smooth wire. Make sure that you clearly mark where all posts are to be placed and don’t forget to mark out your gates.
Gates typically start at 4 foot in length and increase by 2 foot lengths up to 16 feet long. The common exception to this is the standard 3 foot gate. If you space your posts for the size of the gate your gate should be able to swing both ways. For example a 10‘ gate is actually 9’ 6” long so if you space the posts at 10’inside length then you will have approximately 3” space on each side of the gate for a latch and hinges.
To install the posts I recommend using a post driver, whether it is a vibratory driver on a skidsteer or a hammer pounder on a tractor. This, in my opinion is better than digging them by hand or using an auger. You can rent post drivers and machines by the ½ day, whole day or weekend and many contractors will provide you with a quote if you don’t feel comfortable putting the posts in yourself. If you plan to build a wire fence without any boards or rails, you will need to build braces at the beginning and end of straight runs, on both sides of gates and every corner. Brace posts should be spaced at approximately 8 feet.