How To Determine Strike Plate Lip Length

When a frame has decorative trim on the face of the strike jamb a strike plate may need to have the lip length adjusted. It is important to ensure the door lock latches properly and that it doesn’t damage the decorative trim.

To determine the strike lip length required to clear the trim, we can use this formula for extended lip lengths (refer to diagram below):

One half the thickness of the door
+ Inset dimension of the door in the frame
+ Thickness/Projection of trim
+ 1/4″ for curved lip strikes OR 1/8″ for flat lip strikes
= Lip-to-Center (LTC) dimension

Use the manufacturer’s next closest size.

So, let’s use an example to see how this formula would be used:

• We have a door that is 1-3/4″ thick
• The door is inset 1/16″
• The trim is 3/4″ thick
• We have a curved lip strike.

So, using our formula:

One half the thickness of the door (7/8″)
+ 1/16″ inset dimension
+ 3/4″ trim thickess
+ 1/4″ for curved lip strike
= 1-15/16″ LTC

So we would want to use a 2″ strike at this door and frame. This is the Lip to Center (LTC) dimension.

The default lip length for a door that is 1-3/4″ thick and has a 1/16″ inset, with no decorative trim on the face of the frame, is 1-3/16″ lip length.

The inset is measured from the face of the frame to the face of the door on the pull side face of the opening, see diagram below.

Image used from DHI.