Well, I think I know the formula for determining lean body mass (lbm) which should give you an idea of muscle gained (or lost).
A= Weight
B= Body Fat %
The formula is LBM = A - (AxB/100). Sounds confusing, but it isnt that hard.
For instance, if you used to weigh 199lbs, and your bf% was 17.5%, then you would have a lean body mass of around 164.2.
So if you take your measurements again after a month or two, and you weigh 198lbs, but with a body fat & of 13.7%, then your lbm has gone up to 170.8. So with that, I think you can state that you gained about 6 pounds in muscle.
This is the only formula I know about- but someone should chime in if there is a less complicated way of figuring these things out.
