There's a great post that discusses a formula for priming sugar - which gives you more control over your carbonation levels. After searching, I can't find it again. Check the style guidelines for the beer you are brewing for proper carbonation of your style - you have lots more control using priming sugar (confectioner's sugar) - and can probably pick it at your grocery store cheaper than that charged online. Carb tabs are too expensive and don't let you finesse your carbonation levels.
A great tool online is:
It has the recommended CO levels per beer style, and you punch in the other data, including desired CO volumes and it will tell you how much sugar to add. I have not used this calculator, however, so no promises! It is discussed on HBT, here:
If you want to do the calculations yourself using hard numbers, here is the post (which I copied and saved on my computer, which is why I have it, but can't find it on HBT) . . .
Calculations for Bottling Baby Beers
I was looking to find the formula to find the amount of corn sugar for bottling and there was a ton of info out there... I just wanted to put this here since it might help someone in the future.
My formula is (in mixed measurements):
grams of corn sugar = gallons * (volume wanted - volume @ current temperature) * 15.15g
Or in Metric:
grams of corn sugar = Liters * (volume wanted - volume @ current temperature) * 4g
Or all in US:
ounces (weight) of corn sugar = gallons * (volume wanted - volume @ current temperature) * 0.55oz
I used the figures found on this website: http://byo.com/resources/carbonation
I wish the residual CO2 amounts were linear but they aren't.
Let me know if I messed up the math and I'll fix it
Good luck! I'm still learning, too - but carbonation has not been a problem since I started actually calculating it. Your beers will taste more the way you might expect them too, properly carbonated.