[header] How to cut crown molding inside corners [title] Measure the angle of the corner. [step] Use an adjustable protractor to measure the actual angle of the inside corner. Divide this measurement in half to determine the number of degrees each cut will need to be set to. 
[substeps] Place the right side of the protractor against one wall forming the corning. Open up the left side of the protractor, extending it all the way open until it is perfectly flat against the wall on the other side of the corner.