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How to figure out a 45-degree angle

Updated February 21, 2017

If you need to figure out a 45-degree angle and you don't have a protractor handy, you can create a workaround. A 45-degree angle is half the size of right angle, which is 90 degrees. Working with a ruler and a square or other right angle substitute, you can make the angle without any special tools. The 45-degree angle can be useful for projects like painting diagonals on walls, marking trim, or completing crafts and decoration projects. You may want to use the first 45-degree angle you make as a template so that you can use it to mark other angles easily.

Mark a piece of paper (or whatever surface you are working on) with a right angle. Use the square or whatever substitute right angle you have to trace the angle. The back of a pad of paper or even a magazine will suffice.

Measure off a distance (the length is unimportant) from the point of the angle, and mark it on one leg of the angle.

Measure and mark the identical distance on the other leg.

Draw a diagonal line between the two points on the legs of the right angle.

Measure the length of the diagonal line and make a mark at its centre point. Divide the total distance by two to ascertain this measurement.

Draw a line from the corner of the original right angle to the centre point on the diagonal line between the legs of the angle. This bisects the right angle, creating two 45-degree angles.

Things You'll Need

  • Ruler
  • Right angle (such as a carpenter's square or the corner of factory-cut cardboard)
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About the Author

Bill Brown has been a freelance writer for more than 14 years. Focusing on trade journals covering construction and home topics, his work appears in online and print publications. Brown holds a Master of Arts in liberal arts from St. John's University and is currently based in Houston.