How accurate are online BAC Calculators?

Went out drinking a few nights ago and got absolutely plastered. I had a friend with me who counted my drinks. I put in an online BAC calculator the amount I had (8-10 7% drinks, 2 pornstar shots and several drinks I got from friends which I did not calculate) at 130 lbs in the 5 hours I was drinking, apparently I was sitting at 0.33 BAC on the low end. I was not even close to throwing up by the end of the party, still jumping and singing at closing time. How accurate is the BAC calculator?