Is it a normal Vee-belt? If so you may be lucky in a motor factors since such belts are normally sold by length and section width, and somewhere on the old belt it'll probably give this info ..... something like 540 x 9.5.
Looking at the part number, though, perhaps its a "polyvee"type: normally, again, they're sold by length and width and I'd hazard that it's 611mm long by 4PK (4 peaks, I think) width.