How to Bisect an Angle Using a Compass

By Mark Ryan

To bisect an angle, you use your compass to locate a point that lies on the angle bisector; then you just use your straightedge to connect that point to the angle’s vertex.

Try an example.


Refer to the figure as you work through this construction:


  1. Open your compass to any radius r, and construct arc (K, r) intersecting the two sides of angle K at A and B.
  2. Use any radius s to construct arc (A, s) and arc (B, s) that intersect each other at point Z.
    Note that you must choose a radius s that’s long enough for the two arcs to intersect.
  3. Draw line KZ and you’re done.