plumb bob

A plumb bob is a weight with a pointed tip that is attached to a string. The force of gravity causes the weighted line to hang vertically, or plumb. Plumb bobs come in different weights; the most common are 6, 8, and 12 ounces.


plumb bob


To mark a vertical line on a wall:


  • Hang a plumb bob from a chalk-coated string almost against the wall (ideally with a tiny gap). Secure the string at the top, near the wall, with a nail.
  • Steady the weight by hand until it stops swinging and twirling.
  • Leave the weight to find its final position.
  • Hold the weight against the wall and snap the string against the wall to create a vertical chalk line.
  • Remove the chalk line when no longer needed.