How to Use Protractors

Protractors are used to measure angles in a variety of fields. They are most often found in upper elementary and middle school math classrooms, but they also have practical applications, such as navigation. Protractors are available in a wide variety of types and sizes. Students typically use half-circle or semicircle protractors, but they are also available as full-circle, square and rectangle. Military protractors are sometimes divided by degrees and by mils, which is a unit used by artillery gunners to express azimuth. Regardless of the type or scale, they are all used essentially the same way.

Things You'll Need

• Map (to determine azimuth)

Instructions

Measuring Angles

1. Find the vertex of the angle you wish to measure and place the origin of the protractor on that point. The origin is usually marked by a small hole or a printed cross-hair near the center of the protractor.

2. Align the baseline with the bottom line of the angle. The baseline is the line, visible or not, that connects the origin to the mark denoting zero degrees. Rotate the angle or the protractor if necessary.

3. Find the point where the other line of the angle intersects the protractor scale. Extend the line if it is too short to reach the marked section of the protractor.

4. Read the value at the location where the line intersects the scale. That is the size of the angle, which will almost always be measured in degrees.

Finding Azimuth

1. Mark your current location and the location you wish to find the azimuth for on your map. Draw a line connection the two points.

2. Place the origin of either a square or full-circle protractor on the point that denotes your current location. You must use a square or full-circle protractor since azimuth is expressed in measurements for 0 to 360 degrees.

3. Align the base line with the north-south line on the map. Some protractors will only have a horizontal baseline imprinted on them. Align these with the east-west line on the map, but make sure the zero degree mark is in the due north location.

4. Read the value on the protractor scale that intersects the line drawn from your current location to the new location. This is the azimuth to the new location, almost always expressed in degrees.