How to Measure a Door for a Mortise Lock

Updated February 21, 2017

When installing a door lock, avoid setting your it too high or too low. Properly measuring your door for a mortise lock will ensure that your door's hardware will be in the correct place on the door. The lock fits into a square hole in the door. With any home improvement project requiring measurements, measure at least two times to ensure accuracy of your information. The five measurements you need to make are called the stile, door thickness, backset, distance between holes (if applicable) and the height.

Measure the door from the edge nearest where the lock will go to the inside of the door where it comes to the inner panelling or the glass inset. Write this measurement down as the stile of the door.

Place the measuring tape across the thickness of the door where the lock will be placed to note the door's thickness.

Determine the backset by measuring from the edge of the door to the middle of the bottom most pre-drilled hole. Repeat with the upper hole, if your door has two holes.

Find the distance between the middle of the top hole from the centre of the bottom hole by measuring with the measuring tape.

Stretch the tape from the floor to the middle of the bottom most hole for the height measurement.

Things You'll Need

  • Measuring tape
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