@ic-racer where did you find that? I ended up caving and buying the stupid specification to figure it out because I found so many conflicting sources.
According to ISO 732:2000, the width of the film must be between 60.7 and 61.7mm. Most films I've measured have been around 61.2mm. Also, for future reference, the length of the 120 film must be 820mm to 850mm, though others have said the film can be as small as ~790mm.. that might only be for older film that breaks spec though. And finally, to save anyone else from buying this, the thickness of the film and backing paper must be 0.24mm +/- 0.4mm, and the backing paper width must not exceed 62.90mm, though there is no specification for the minimum size other than "it should cover the film".
And for future internet people, the length of 220 film is between 1651mm and 1700mm. The width is the same as 120
If anyone has any other info they want from the spec, just ask and I'll publish it here.
Other fun facts I didn't even know were in any specification:
B/W film has no standard edge markings on the "exposed" backing paper. Color negative (C-41) has squares around the edge. Color reversal (E-6) has + signs/crosses.
The sealing sticker to close the exposed roll should have some kind of color on it for color negative or color reversal, and should have no color on B/W film
edit: I also updated wikipedia to include this for US/english version anyway