Radian

Pronunciation: /ˈreɪ diən/ ?

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Manipulative 1: Radian measure. Click on the blue point in the manipulative and drag it to change the figure.

A radian is a unit of measure for rotation around a point. 2π radians is the same rotation as one complete rotation about a circle. The abbreviation for radians is rad.

Common angles in radians and degrees

DegreesRadiansPortion of
Full circle
0 rad.none of a full circle
30°pi/6 rad.1/12 of a full circle
45°pi/4 rad.1/8 of a full circle
60°pi/3 rad.1/6 of a full circle
90°pi/2 rad.1/4 of a full circle
180°π rad.1/2 of a full circle
270°3pi/2 rad.3/4 of a full circle
360°rad.One full circle
Table 1: Common angles in radians and degrees

How to convert radians to degrees

One complete rotation about a circle is 2π rad. or 360°. This means 2π rad. = 360°. So, the conversion factor is 360 degrees/2pi radians = 180 degrees / pi.. Example: Convert pi/2 radians to degrees. (pi/2) rad. * (180 degrees/pi) = (pi@crossed out@/2) rad. * (180 degrees)/(pi@crossed out@) = (180/2) degrees = 90 degrees.

How to convert degrees to radians

The conversion factor for degrees to radians is 2pi radians/360 degrees = pi rad./180 degrees.. Example: Convert 45° to radians. 45°*(pi rad)/(180 deg) = 45@crossed out@ °*(pi rad)/(4*45@crossed out@ degrees) = pi/4 rad..

More Information

  • McAdams, David. Angle. allmathwords.org. Life is a Story Problem LLC. 2009-03-12. http://www.allmathwords.org/article.aspx?lang=en&id=Angle.

Cite this article as:


Radian. 2010-12-06. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/r/radian.html.

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Revision History


2010-12-06: Initial version (McAdams, David.)

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