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:
http://hbd.org/cgi-bin/recipator/recipator/carbonation.html?10529930#tag
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:
https://www.homebrewtalk.com/f35/carbonation-calculator-88961/
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) . . .
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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
M_C
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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.