I have a Fat Scale which measures my weight, body fat %, muscle mass, bone mass, BMR, AMR etc. Its beurer BF-750. The problem with this machine is if I set my activity level different it shows my body fat % totally different. Only thing which is almost always same on all activity level is BMR. Is there any formula to calculate body fat % using BMR on my own?
The Katch-McArdle Formula (Resting Daily Energy Expenditure):
P = 370 + (21.6 * LBM)
Where LBM is your lean body mass, and
LBM = BM * (1-BF)
where BF is your bodyfat ratio.
Although both the BMR and the BF values you get from your scale are very imprecise. BMR is probably calculated using something like harris and benedict formula.