For double hung sash: When both top and bottom sash are required, measure the distance between the side jambs (this should normally be 4" larger than the glass size width) and the distance from the bottom of the head jamb to the point on the sill where the outside of the bottom rail touches.

Single sash: When only one sash is required, it is a good idea to give the outside, or overall dimensions of the existing sash and the glass size.

Storm or screen: Measure the distance between the side casing of the window unit and measure from the bottom of the head casing to the top of the outside or sub sill. If it is for a double hung window, give the measurement from the bottom of the head casing to the center of the crossbar. The glass size of the storm window in most cases is the same as the glass size for the window it is designed to cover.

Dimensions are always given as width first, followed by height.

Cross bar height: measure top of sash to center of inside sash.

Also need degree of bevel (angle) usually between 5 degrees to 14 degrees.

Specify whether the actual sash has been measured or a rough opening.