Really the answer to this question depends on the thickness of your blade - information which many manufacturers do not publish, Butterfly being a notable exception to this ( their catalogue gives this information and also the overall dimensions of each blade and handle.) If the blade is 6mm or more thick then you will generally be fine with 12mm edge tape, but if it is thinner ( my second blade is only around 4mm thick ) then 10 mm or 9mm edge tape is required. You don't really want the edges of the tape to protrude beyond the surface of the rubbers.
When I re-rubbered my second blade back in January I had no clue which thickness of tpe to buy so I bought a short length of both 12mm and 9mm. This was easy when dealing with Tees Sport since they sell their own edge tape in 3-bat lengths, whereas I have found that some other vendors only appear to be interested in selling you a 50m roll of the stuff. I managed to get a shorter length of Joola edge tape for my K7 - I think the roll I have would do seven or eight bats - but only by buying from Germany through Amazon, it certainly didn't come from Bribar.