How do you measure a picture frame molding?

Measure the length and width of the picture frame molding one-eighth inch larger than the item to be framed. Double the measurement of the grooves cut into the back edges of the molding, and subtract this amount from the first measurement before cutting the molding.

The grooves cut into the back edges of molding are called rabbets. Rabbets allow room for the glass and backing to lay flush against the back of the molding. This prevents it from standing out from the wall. The corners of picture frame molding are generally cut on a 45-degree angle, with the longer edge of the angle matching the measurements given.