How do I Measure to Fit a Mortice Sash Lock?

Written by brian scudder
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How do I Measure to Fit a Mortice Sash Lock?
Contemporary mortise lock (lock image by Gonçalo Carreira from

Mortise, or mortise, sash locks are a type of lock used to secure doors and windows, where a mortise is cut into the edge of the door to house it. Measuring for a mortise lock requires marking dimensions on the door for the lock body and latch plate along with holes drilled in the faces of the door to accept knob handles. Most mortise locks are installed between 37 and 40 inches off the floor to the centre of the lock.

Skill level:

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Things you need

  • Tape measure
  • Utility knife
  • Mortise lock paper template

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  1. 1

    Mark the edge of the door on the opposite side of the hinge by measuring vertically from the floor and placing a pencil mark at 38 inches.

  2. 2

    Measure the length of the latch plate and divide the measurement by two. The latch plate is the metal plate that will be installed after the lock is fastened in the mortise.

  3. 3

    Mark the dimension result on the edge of the door from the top and bottom of the 38-inch mark. These marks will be the top and bottom of the latch plate.

  4. 4

    Center the latch plate on the door edge with the top and bottom aligned on the marks.

  5. 5

    Screw the latch plate on the door edge with the screws provided.

  6. 6

    Score around the perimeter of the latch plate with the utility knife and remove the screws and latch plate.

  7. 7

    Mark a vertical centre line on the edge of the door in the area that was scored for the latch plate. This mark is the vertical centre of the mortise.

  8. 8

    Place the template provided with the mortise lock on the 38-inch mark on the door.

  9. 9

    Mark the holes for the door handles on both sides of the door with a pencil.

Tips and warnings

  • Accurate measurements are critical for proper operation of the mortise lock.
  • Mark front and back of the door lightly with a pencil in case the marks must be erased and moved.

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