How to Use Batter Boards to Square Corner Posts for Deck

Measure out from the wall of your home to the planned location of one corner of the deck.

Drive three 2-foot tall, 2-by-4 inch stakes into the ground, forming an L-shaped right angle about 2 feet to the outside of the approximate location where you plan on placing the first post. Nail two 1-by-6 inch boards between the stakes, 12 inches above the ground to complete the corner. These are the batter boards.

Place another set of batter boards outside the planned location of the second post.

Attach a string to the house at the end point of the deck. Stretch it out so it's over the approximate location of the first post and tie it to the batter board so the string is tight.

Tie a second piece of string to the batter board at right angles to where you tied off the first string and stretch it across the first string to the second batter board. Run a perpendicular string from the second batter board to the side of the house. You'll now have a rectangular arrangement of strings, with the home's wall as one side of the rectangle.

Measure the distance across the rectangle -- wall to opposite string intersection in both directions. Adjust the location of the strings along the batter boards until the measurements are equal -- this will square the rectangle. Mark the ground below the string intersections for the post locations.