Couple of things to note:
1. American Red Cross suggests 4 drops per liter or quart. But there is no need to get too scientific. Anywhere between 4 and 8 is probably fine.
2. Bleach (and iodine too) won't kill some of the bigger baddies -- like certain protozoa (e.g. crypto) -- at least not in the dosage that you can still tolerate drinking afterwards.
3. Some hikers choose chlorine dioxide instead -- as that can kill all three classes of biological baddies: viruses, bacteria, and protozoa. HOWEVER, the chemicals work sluggish in cold water -- so treatment time can range from 30 minutes (room temp) all the way to 4 hours (for water just above freezing). Since few of us are ever willing to wait this long in the middle of the day, I see this as a false sense of security.
If you are concerned about protozoa, then I highly recommend combining chemical treatment (bleach) with a simple filter. Let bleach work on the tiny and easy to kill stuff -- then use a simple filter block out the big stuff. AquaMira Frontier Pro filter weighs only 2 ounces! In addition to blocking protozoa, it will clarify your water and its carbon core will improve water taste as well -- including the removal of any residual chlorine taste.