How to Calculate Angle Degrees

A protractor makes the task of measuring angles simple.

Angles are everywhere, and it's easy to look them over in everyday life without a second thought. Then curiosity strikes--perhaps in the form of a geometry class--and suddenly you need to figure out exactly how many degrees are in an angle. This article walks you through some easy steps to do so. First, it will explain some basic angles that can be recognized at a glance. Then, it will teach you how to use a tool called a protractor by lining it up to your angle and reading your results. Whether you're a geometry student, an artist, or simply a curious mind, you'll figure out angles in no time.

Things You'll Need

• Protractor

Instructions

Recognizing Basic Angles

1. Learn to recognize certain angles by just looking at them. For instance, if your angle is a straight line, you should know right away that it is 180 degrees. It is a straight angle. If your angle looks like the corner of a sheet of computer paper or the corner of a square, it's easy to tell that the angle there is 90 degrees--half of 180. It is called a right angle.
   There are two other types of angles. Angles that are smaller than 90 degrees--which is the angle formed by the corner of a square--are acute angles. Angles that are larger than 90 degrees are obtuse angles. Learning to recognize these angles at a glance is the fastest way to figure out the number of degrees in these angles.

2. Use a protractor for angles that cannot be recognized at a glance. The bottom of the protractor has a straight edge or a straight line, and a line or dot to indicate the center. Line up the straight edge and the center dot with the angle you are measuring. Make sure to put the dot at the place where the two lines in your angle cross.

3. Read your results. If everything is lined up correctly, one leg of your angle should point to the round edge of your protractor. It may even extend beyond your protractor. Lining the round edge of your protractor are a lot of numbers, and that edge can be read just like a ruler. What number does our your line fall at? That is the number of degrees in your angle.

4. Double-check to make sure you read the correct number. Depending on which side your angle opens up to, you could either be reading the correct number, or you could be getting its sister angle, which is 180 degrees minus your angle.
   An easy way to check if you read the protractor correctly is to see if your angle is an acute angle or an obtuse angle. If your angle is acute and you're reading a number of degrees that is more than 90, you are reading the wrong number. The same thing is true if your angle is obtuse and you're reading a number of degrees that is less than 90.

Tips & Warnings

• Even if you read the wrong number, just remember that 180 minus the number you got will give you the correct number of degrees in your angle. Just practice and soon measuring degrees in angles will be a cinch!