Degrees

Definition: A measure of an angle. One degree is one 360th part of a full circle.
Try this Adjust the angle below by dragging the orange at R. Note the number of degrees for any particular angle.

Measure of an angle

In geometry, an angle. is measured in degrees, where a full circle is 360 degrees. A small angle might be around 30 degrees. Usually, when a finer measure is needed we just add decimal places to the degrees. For example 45.12°

The small circle after the number means "degrees". So the above would be pronounced "forty five point one two degrees".

Degrees - Minutes - Seconds

When measuring things like latitude and longitude, each degree is divided into minutes and seconds. The degree is divided in to 60 minutes. For even finer measurements the minute is divided again into 60 seconds, However this last measure is so small, it only used where angles are subtended over extreme distances such as astronomical measurements, and measuring latitude and longitude.

These minutes and seconds have (confusingly) nothing to do with time. They are just smaller and smaller parts of a degree.

See also Degrees - Minutes - Seconds calculator for a calculator that can add and subract angles in this form.

Unit Written Pronounced
Degrees With a small circle after the number.
Example 61°
"61 degrees"
Minutes With a small dash after the number.
Example 34° 21'
"34 degrees, 21 minutes"
Seconds With two small dashes.
Example 32° 34' 44''
"32 degrees, 34 minutes, 44 seconds"
When minutes and seconds are used alone, we usually say "arc minutes" and "arc seconds" to avoid confusion with time units.

Which direction to measure?

In the figure above, adjust the point R so the line crosses the point marked 315°. Starting at Q and going counter-clockwise we see the measure is 315°. But if we were to go clockwise from Q it would be 45° (360-315). Which is correct?

They both are, but by convention the smaller one is assumed. That is why the angle at the center shows 45° under these circumstances. The larger measure (315°) is called the reflex angle RPQ.

Angles you should know

Use the figure above to become familiar with what various angle measures look like when measured in degrees. In general, you should be able to visually estimate any angle to within about 15°, and you should be able to recognize the common angles (shown in red) on sight and sketch them yourself.

Other measures

Things to try

  1. In the figure above, click on 'hide details'.
  2. Adjust the position of the point R
  3. Estimate the measure of the angle RPQ
  4. Click 'show details' to see how close you got
  5. Repeat.

You should especially be able to estimate angles close to the red ones in the figure above, since they appear frequently in geometry.

Other angle topics

General

Angle Types

Angle relationships