Mobile home windows are manufact
Mobile home windows are manufactured in standard sizes.

To find the measurement for a mobile home window, it is important you know that mobile home windows (and Doors) get their "Call Size" (what you order) from the “Rough Opening” or size of the hole in the wall. This means that normally the windows are not measured on the outside or by using the outside edges of the window, but by the inside.

Generally, mobile home windows are produced in standard sizes, making measuring for replacement windows easier. By getting a very close measurement, your mobile home parts supplier (B&H :-) can help you determine the size windows you need for replacements.

TIP:
Some mobile homes have two windows, a storm window inside, and a single pane window outside. Use the same measurement for both windows when replacing them.

Standard Window Widths are... 14",18",22",24"30",36",40", & 46". 

The most common are... 14",30", & 46"

Standard Window Heights are... 8",21",27",30",36",38",40",52",53",54",58",60",62",66", & 68"

The most common are ...21", 27", 30", 40", 53", & 54"

Some times it is easier to get the "Call Size" by measuring the outside of the window, including the screw flange. Subtracting 1 1/2" from the measurment should get you there.