How to Check for Plumb

Carpenter’s Level

• 1

  Place a carpenter’s level against the side of the post, framing lumber or other object you wish to check. The longest level you can use will provide the most accurate measurement. A 36- or 48-inch carpenter’s level works well for construction projects.

• 2

  Look at the position of the air bubble in the oil-filled glass sighting tube on the carpenter’s level. Note where it is in relation to the scribe marks on the tube. The object is plumb when the air bubble is precisely centered between the two scribe marks.

• 3

  Place the level on an adjacent side of the post, framing lumber or other object, and check for plumb in that direction as well. An object may be perfectly plumb in one direction but off in the other direction.

• 4

  Adjust the post, framing lumber or other object until the air bubble is centered in the tube for the adjacent sides.

Plumb Bob

• 5

  Tie a plumb bob's string to a fixed point above and next to the object you wish to measure for plumb. The bottom of a floor joist or a ceiling is a good spot to locate the string. You may hammer a nail into a joist or the bottom of a subfloor if nothing else is available to tie off the string.

• 6

  Lower the weighted end of the plumb bob so it is about 1/2 inch off the floor. Steady the bob so the string stops swaying.

• 7

  Measure the distance from the string to the object to be plumbed at the top of the object and near its bottom. If the two measurements are equal, then the object is plumb. If they are not equal, adjust the object and repeat the measurement process.

• 8

  Check for plumb on the adjacent side of the object in the same manner.