"hello, i have what used to be a double pain window split in middle like most, one side measures 47 1/2 inch and other length frame edge to edge measures about the same. One side on half window had 1 of the single pains broke out so its just single pain on one half now on this measurement, How much approx to replace, how common is this size for a house, and if you usaullly order this size, how long does it take to order and complete this small job?" in Yahoo! Answers
Or perhaps you can go on using the window with just the one pane - I've done that when I didn't need a thermopane window.
Otherwise, take your measurement and go to the glass shop and have them make you up another therompane.