Measure out 3 feet away from the corner of one wall and make a mark.
Measure out 4 feet from the corner on the adjacent wall and make a mark.
Measure the distance between the two marks. If the measurement between the two marks isn't 5 feet, the wall isn't square.
Set the level against the wall horizontally. If the wall is square, you'll find the bubble in the center markings of the level. Retest the wall going up a few feet and then down a few feet to ensure the placement of the bubble in the level.
Set the level against the wall vertically. If the wall is square, you'll find the bubble in the center markings of the level. Retest the wall going over few feet left and right to ensure the placement of the bubble in the level.
Place a carpenter's square in the corner where two walls meet. If the square sits flush in the corner two adjacent walls are square. Retest the carpenter's square up and down the corner to ensure the carpenter's square sits flush in the corner.
Things You Will Need
- Tape measure
- Carpenter's square
- Although builders try to get walls square in a home, it doesn't always happen. You may need to use shims to adjust the angle of the wall before applying bead board, plywood or dry wall to studs.