Lay the trousers flat, and straighten out the waistband, before measuring edge to edge.
Measure from the bottom of the waistband to the edge of the crotch seam.
Lay the trousers flat, then measure across the thigh about 2cm below the crotch.
Measure 40cm down the inside leg seam of the trouser - then flatten the leg and measure across the knee at that point
Lay the leg flat and measure across at the leg opening.