I'll do you one better. The US navy devised a formula based on height age and your neck and waist circumference and was 2-4% accurate for body fat calculation

I'll do you one better. The US navy devised a formula based on height age and your neck and waist circumference and was 2-4% accurate for body fat calculation (it's not good for tracking relative changes tho). You can make generally fairly accurate assumptions about body fat percentage from a few key indices when it comes to general population. The electrical impedance issue becomes more problematic when you have a higher muscle mass vs fat mass as the scale has a much harder time figuring that out (which is why some of the scales have an "athlete" mode on them). Most of the good scales also have a handheld impedance sensor on them to track upper and lower body impedance for a more accurate measurement tho.