Seat Measurements
Empty pockets before you take the measurement, which should be around the fullest part of the seat, hold the tape to allow the fingers to slide.

Inside Leg Measurements
Adjust trousers to a comfortable position, and measure from the highest point of crutch to hem

Outside Leg Measurements
Adjust trouser to normal waist position, and measure from top of waistband to the top of the foot.
The normal difference between the inside leg measurement and the outside leg measurement is 10"