Understanding your BMI
Body Mass Index estimates how your weight relates to your height. It's a quick screening tool used by doctors and health organizations worldwide to flag whether someone falls into an underweight, healthy, overweight, or obese range — not a diagnosis on its own.
The formula behind the number
BMI is your weight in kilograms divided by your height in meters, squared. In pounds and inches, multiply your weight by 703, then divide by your height in inches squared. Either way, the result lands you in one of four bands.
What the categories mean
These four BMI bands are the same for men and women — the World Health Organization doesn't set separate cutoffs by sex. What does differ by sex is how much of that weight is typically body fat, since women naturally carry more essential fat than men at the same BMI.
- UnderweightBelow 18.5
- Normal weight18.5 – 24.9
- Overweight25.0 – 29.9
- Obese30.0 and above
Healthy body fat range, by sex
Your body fat estimate above uses the Deurenberg formula, which factors in your BMI, age, and sex. Here's how that number is generally read for adults, based on American Council on Exercise reference ranges:
| Category | Women | Men |
|---|---|---|
| Essential fat | 10 – 13% | 2 – 5% |
| Athletic | 14 – 20% | 6 – 13% |
| Fitness | 21 – 24% | 14 – 17% |
| Acceptable | 25 – 31% | 18 – 24% |
| Above average | 32%+ | 25%+ |
Body fat estimates from any formula are approximations — for a precise reading, ask about DEXA, BodPod, or bioelectrical impedance testing.
Frequently asked questions
Does BMI account for muscle mass?
No. BMI only uses height and weight, so it can overestimate body fat in very muscular people and underestimate it in people with low muscle mass. Treat it as a general screening tool, not a diagnosis.
What's a healthy BMI range for adults?
For most adults, a BMI between 18.5 and 24.9 falls in the normal weight range. Ranges can vary slightly by age, sex, and ethnicity, so use this as a starting point rather than a final answer.
Is BMI calculated differently for children?
Yes. Children and teens are measured against age- and sex-specific percentile charts instead of the fixed adult categories, since body composition changes as they grow.
Why do men and women have different healthy body fat ranges at the same BMI?
Women's bodies store more essential fat to support reproductive function, so a body fat percentage that's healthy for a woman would be considered low for a man, and vice versa. BMI itself doesn't capture this — it only sees total weight and height.