I took almost a year off lifting, put an inch on my arms in a month and have put on about .2 inches in the last 5. Trust me you arn't going to be able to get to 16" in 4 months.
Thanks a lot for the comments everyone. I have gained about 10lbs, probably of which is about 1-2lbs of fat, so.. I've gained about 5lbs of muscle. And the other 3-4lbs is water weight.