Classic BMI
26.5
CAUTION
18.5 – 24.9
The 190-year-old population statistic. Useful context, terrible at telling muscle from fat.
Know Your Body · Steward It Well
BODY COMPOSITION.
BMI was invented in 1832 by an astronomer studying populations — not people. It cannot tell muscle from fat and it punishes tall frames. This runs the modern set: waist-to-height, Body Roundness Index, ABSI, Relative Fat Mass, FFMI and your resting burn. Add a waist measurement and the accuracy jumps dramatically.
Your Measurements
UNITS
SEX AT BIRTH
A tape measure beats a scale. Waist at the navel, relaxed — no sucking in. These unlock the metrics BMI can never give you.
CLASSIC BMI
26.5
CAUTION
BODY FAT
22.8%
RELATIVE FAT MASS (DXA-VALIDATED)
WAIST / HEIGHT
0.49
TARGET UNDER 0.50
New BMI (Trefethen)
25.9
CAUTION
18.5 – 24.9
Scales with height^2.5 instead of height^2, so tall frames stop getting falsely flagged.
Waist-to-Height
0.49
OPTIMAL
under 0.50
Keep your waist under half your height. Best simple predictor of metabolic risk there is.
Body Roundness Index
3.09
OPTIMAL
2.0 – 4.5
Treats your body as an ellipse. Tracks visceral fat — the dangerous kind around your organs.
A Body Shape Index
0.0728
OPTIMAL
under 0.081
Isolates waist risk from body size. High ABSI means risk even at a 'normal' BMI.
Body Fat
22.8%
CAUTION
8 – 19%
Estimated by Relative Fat Mass (DXA-validated). No pinching, no calipers, no lab.
Lean Mass
64.8kg
build it
Everything that isn't fat: muscle, bone, organs, water. This is the number to grow.
Fat-Free Mass Index
20.5
19 – 22 trained
Muscularity independent of height. The number BMI should have been for athletes.
Resting Burn
1780kcal/day
baseline
Mifflin-St Jeor. What you burn doing absolutely nothing but existing.
These are estimates for training guidance, not a medical diagnosis. Trends over weeks matter far more than any single reading — take measurements at the same time of day, same conditions.