Construct the Perpendicular Bisector of a Segment Using a Compass

By Mark Ryan

To construct a perpendicular bisector of a segment, you use your compass to locate two points that are each equidistant from the segment’s endpoints and then finish with your straightedge. The following example shows you how it’s done.


This figure should help as you work through the construction process:

Constructing a perpendicular bisector.
  1. Open your compass to any radius r that’s more than half the length of segment CD, and construct arc (C, r).
  2. Construct arc (D, r) intersecting arc (C, r) at points G and H.
  3. Draw line GH. You’re done: line GH is the perpendicular bisector of segment CD.