A tape measure is an estimate — about three to five points either way against a DEXA scan. Measured the same way each time, the direction it moves is the part to trust.
Report card
Lean mass—
Shoulder to waist—
The classical reference is about 1.6. This is worked out from the waist at your navel, so it reads a little lower than a ratio taken at the narrowest point — and it is an aesthetic measure, not a health one.
Waist to hip—
Under 0.80 is where the WHO puts a woman's low-risk range. Measured from the waist at your navel rather than the WHO's rib-to-hip midpoint, so it reads a touch high.
FFMI—