How to create a straight line of fence posts is a mystery to many uninitiated fence builders. Creating one straight line can be a challenge, but lining up a 90-degree angle for your corners is really tough without the proper information. There are two tricks that have been used over the years in building. To establish straight lines, tie a string between two fixed points in line with your wall or fence. To create a 90-degree corner, use the rule of 3-4-5. These two quick tricks will give you the power to put your fence posts where you want them every time.
Find out where your property line runs, or decide where the corners of your fence will be. Drive in a wooden stake where each corner post will be. Use a 3 pound hammer to set the post firmly in the soil.
Tie a piece of mason's line tightly between the two stakes. Measure from one post, and wrap a piece of tape around the mason's line every 8 feet, for traditional spacing, or at every interval you plan to place a post.
Hang a plumb bob 1 or 2 inches above the ground, lined up with each piece of tape on the line. Wait for it to stop moving, and mark the spot below it with a squirt of chalk line chalk, from the bottle. This will mark your fence post holes at precise intervals, along a straight line.
From one of your stakes, measure the distance to the next corner. Make it as close to a 90-degree angle as you can. Place a third stake here, and tie a line between it and the original corner stake. Do not drive it into the ground. Have a helper hold it in position the correct distance from the third stake with the line taut.
Measure from the original corner stake along the first line you laid out to a point 3 feet down the line, and wrap a piece of tape around the line to mark the spot. Measure from the original stake down the new line, and mark a spot 4 feet from the stake.
Stretch your tape measure between the two spots. The distance should be 5 feet. Tell your helper to move the line out to widen the angle, if the distance needs to be increased, or move the line in to narrow it, if the distance needs to decrease. Adjust the line until it there is exactly 5 feet between the two points, and drive the stake into the ground.
Measure along this line and mark positions for posts as you did the first line.