Basically Iam, what they are trying to say is that it is impossible to answer that question. It will vary based on your genetics, muscle belly size & shape, training methods, etc.
The average lean US male that doesnt work out has a 10-14" arm. The blood pressure/heart rate testers at Wal-marts are made to accomodate a 9"-13" arm.
Go out, get a tape measure, measure your arms. Then make sure you have a solid training routine and diet, then get plenty of rest. You will make good gains.
We can all help you with your training if you give a little bit of background info. What are your stats (Ht, Wt, BF%)? How long have you been training? When do you like to train?