sugar carbonation question

so I have just bottled my first beer, a nice porter. According to the kit, 5oz of corn sugar is what I should use for carbonation on my 5 gallon batch.

I have 2 questions...

1. I planned on having 5 gallons of beer, which is roughly 53 beers... but I only ended up with 42 beers from my batch. Do I have 42 hand grenades?

2. Is there some other way to decide how much corn sugar I should use, or a link that someone could point me towards?

I have gotten anywhere from 41(first batch) to 49 beers from a 5 gallon batch depending on how much you loose between transfers and gravity reading. I always used the 5oz sugar and haven't had a bomb yet.

Excellent, that's what I wanted to hear. Thanks.

There are a bunch of calculators. Here is one,
http://www.tastybrew.com/calculators/priming.html

I make 5.5 gallons and usually get exactly 53 12 oz bottles.