The short version
- BMI was never designed for athletes. Adolphe Quetelet introduced the formula in the 1830s as a population statistic, not an individual diagnostic.
- Muscle is denser than fat — about 15% more — so at the same height, a muscular person weighs more than a sedentary person of the same build.
- Use body fat % and waist measurements instead if BMI flags you as overweight. They capture what actually matters for health.
Why a BMI of 28 can be perfectly healthy
Rugby players, CrossFitters, bodybuilders, and Olympic lifters routinely sit in the “overweight” (25–30) or even “obese” (30+) bands of BMI while carrying body fat in the low teens or single digits. A typical example:
- A 180 cm man weighing 92 kg has a BMI of 28.4 — firmly “overweight”. If his body fat is 12%, he carries 11 kg of fat and 81 kg of lean mass. That's a lean, athletic physique, not a health concern.
- The same BMI in a sedentary man with the same height and weight might correspond to 28% body fat — 26 kg of fat, 66 kg of lean mass. The health picture is completely different.
BMI can't see the difference, because the formula has no information about body composition. It's a blunt instrument that works reasonably well at population scale and fails predictably for the ends of the fitness distribution.
Where BMI fails hardest
- Strength and power athletes. Rugby, American football, powerlifting, Olympic weightlifting, bodybuilding — high muscle mass pushes BMI up independently of fat.
- Anyone lifting consistently for 2+ years. You don't have to be an elite athlete to outgrow BMI's assumptions. Sustained strength training shifts the ratio.
- Short, stocky, or mesomorphic builds. BMI divides by height squared, which penalises shorter people disproportionately at the same body composition.
What to use instead
- Body fat % estimator — the U.S. Navy circumference method takes neck, waist, and (for women) hip measurements and returns an estimate within ~3–4 percentage points of DEXA for the general population. Good enough to tell a lean-muscular 28 BMI from an overweight 28 BMI at a glance.
- Waist-to-height ratio — a single waist measurement divided by your height. If your BMI is high but your waist is well under half your height (i.e. WHtR < 0.50), central adiposity is not the problem.
- Performance and function. If you can run, lift, and recover well, your resting heart rate and blood pressure are healthy, and your blood work is in range — your BMI number is noise, not signal.
When BMI still tells you something
Don't throw BMI out just because you lift. It's still useful as a tracking number if you watch your own trend rather than comparing to population cut-offs. A BMI that drifts up by 2–3 points over a year at the same training volume is worth noticing — it's usually fat gain, not muscle. A stable or slowly-rising BMI during a focused strength block with a stable waist is exactly what you'd expect.
Use the BMI calculator with context
The BMI calculator's Personalize result panel lets you flag athletic or muscular build and see the limitation called out directly on the page. For a real answer, run the body fat estimator and the waist-to-height ratio alongside it.
Measuring correctly
If you're reaching for a tape measure, see how to measure your waist correctly— a small mistake on tape placement moves the result more than the calculators do.
Medical disclaimer. This article is for general educational use and is not medical advice. If you have concerns about your weight, body composition, or cardiovascular health, discuss them with a qualified healthcare professional.