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How to Measure for the Squareness of Walls

When builders use the words "square" or "plumb," they are referring to the angle of the walls. Walls set at a proper 90 degree angle are easier to apply boards to and are stronger than those that aren't 90 degrees. Determining if a wall is square isn't necessarily difficult. You can use the Pythagorean theorem (a2+b2=c2) to ensure the walls are square or use carpenter's tools such as a carpenter's square and level. Longer levels yield more accurate results, so if you're using the level method, use the longest level you can find.

Pythagorean Theorem

Ensure walls are square before construction or home improvements.
  1. Measure out 3 feet away from the corner of one wall and make a mark.

  2. Measure out 4 feet from the corner on the adjacent wall and make a mark.

  3. Measure the distance between the two marks. If the measurement between the two marks isn't 5 feet, the wall isn't square.

Carpenter's Tool

  1. 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.

  2. 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.

  3. 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.

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