Body composition
BMI calculator
Calculate body mass index from your height and weight, a number that often comes up alongside a low testosterone workup.
How this calculator works
BMI equals weight in kilograms divided by height in meters squared. For imperial units, that's weight in pounds times 703, divided by height in inches squared. This tool applies whichever formula matches your selected unit system.
The standard categories
Under 18.5 is classified as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or above as obese, per WHO and CDC definitions. These are population screening categories, not an individual diagnosis.
Why this connects to testosterone
Adipose (fat) tissue contains aromatase, the enzyme that converts testosterone to estrogen, which is one mechanism linking higher body fat to lower measured testosterone. That's part of why clinicians often review weight and BMI alongside a low testosterone workup, not in isolation.
Frequently asked questions
How is BMI calculated?
Body mass index is weight in kilograms divided by height in meters squared. In imperial units, it's weight in pounds multiplied by 703, divided by height in inches squared. Both formulas give the same result.
What do the BMI categories mean?
The World Health Organization and CDC define under 18.5 as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or above as obese. These are population-level classifications, not a judgment about any individual's health.
Why does BMI come up in a TRT context?
Higher body fat is associated with lower testosterone through several pathways, including increased conversion of testosterone to estrogen in fat tissue, which is part of why BMI is often reviewed alongside a low testosterone workup. BMI is also one of the eight criteria in the STOP-BANG sleep apnea screener.
Is BMI a perfect measure of health?
No. BMI doesn't distinguish muscle from fat, so it can overestimate body fat in very muscular people and underestimate it in people with low muscle mass. It's a simple screening number, not a complete health assessment.