Back Button

How to Check a Room's Squareness

Michael Logan

A room's squareness is defined by how parallel the walls are and also how close to 90 degrees the corners are. This is useful when framing a new room or remodeling an existing room with moldings, floors and some wall treatments.

Check a room for squareness before beginning a remodeling project.

Knowing what to expect when you work in the corners on a remodeling project is helpful, especially with floors and moldings. You can check a room's squareness with a few simple tools.

  1. Measure between two diagonal corners, then measure between the other two diagonal corners. Compare the two measurements. The closer the measurements are to each other, the more square the walls and corners are.

  2. Place the square in the corner with one leg on one wall, and the other leg on the adjoining wall. If there is a gap between the point of the square and the corner, the corner angle is less than 90 degrees. A gap between one leg and one wall indicates the angle is greater than 90 degrees.

  3. Measure the length of opposite, parallel walls. If the wall measurements don't match, you'll find the corners won't measure 90 degrees.

  4. Measure 3 feet from the corner on one wall and make a mark. Measure 4 feet along the adjoining wall and make a second mark. Measure diagonally between the two marks. If the diagonal measurement is less than 5 feet, the corner angles is less than 90 degrees. A measurement greater than 5 feet means the corner angle is greater than 90 degrees.

  5. Tip

    Use your findings to make adjustments for strip flooring, moldings and wall treatments like bead-board or frame and panel wainscot. By making allowances for walls that are out of square, you can minimize the visual effect they have on building materials that make a pattern. Cope cut moldings for inside corners instead of miter cutting them in out of square rooms. The moldings look perfect and you don't have to worry about angles that are not 90 degrees.


    Don't worry about rooms that are not perfectly square. The building process for homes is such that walls and rooms are rarely perfect. The finish materials usually make up for any imperfections.