The only real answer is to get a good set of calipers (digital by
preference) and measure your sawblades. Then find a drillbit just a
smidge larger. (Imperial smidge. Be careful you don't use the old
French Smidgeaux, or the metric Smidgiter. They're different, and
the cross calculations are painful.)
Silliness to the side, the teeny drills (at least in the US) are
sized by wire gage (Naturally, it's not the same wire gage we use
for precious metal wire, so no joy there. The numbers don't mean
anything to us beyond 'this one's bigger than that one'.) They're
called 'number drills'. You can pick them up in better hardware
stores, and there are online cross references. So if you know that
your sawblade is.019" at its thickest, you can tell that a #75 or
#76 drill would work.
(Wikipedia page here: http://www.ganoksin.com/gnkurl/ep802b
inch/mm conversion chart is about half way down the page. (along with
much more than you ever wanted to know about how we ended up with
such a screwy system in the first place.)
The big trick is getting a good caliper so you can measure your
blades in the first place. Without that, none of the rest matters.
Unfortunately, there's enough variation between sawblade sizes and
manufacturers that there's no point in saying that a 2/0 blade is
any particular size, and calling that a standard. You need to
measure the blades in front of you, and go from there.