What is a healthy BMI for adults?

The WHO healthy band runs 18.5–24.9. Below 18.5 is underweight; 25–29.9 overweight; 30+ obesity. It is a screening range, not an individual target.

Is BMI calculated differently for men and women?

No — the formula is identical. Body-fat percent differs by sex at the same BMI, which is one of the measure’s known blind spots.

Is BMI accurate for athletes and bodybuilders?

Not really. Muscle is denser than fat, so lean, muscular people often score “overweight” while carrying little fat. Use body-composition measures for athletic populations.

Your BMI divided by 25. The healthy band is roughly 0.74–1.00: 0.60 signals underweight just as surely as 1.30 signals overweight; 1.10 means you are 10% over the ceiling.

Why do Asian populations use different thresholds?

At the same BMI, several Asian populations carry more abdominal fat and face metabolic risk earlier, so clinical guidance often uses 23 and 27.5 as cutoffs.

Can children use this calculator?

No. Under age 18, BMI is compared against age-and-sex growth percentiles (BMI-for-age), a different chart entirely.

BMI Calculator | Online Calculators Free

What BMI measures

Body mass index divides weight by height squared (kg/m²), which makes tall and short people comparable on one scale. Adolphe Quetelet devised the ratio in the 1830s; the WHO's cutoffs (18.5, 25, 30) date from 1995–1997 expert consultations and remain the international default.

The formula and its variants

Metric: BMI = kg ÷ m². Imperial: BMI = (lb ÷ in²) × 703.07 — the constant converts pounds-per-square-inch to kilograms-per-square-meter (0.45359237 ÷ 0.0254²). BMI Prime divides your BMI by 25: 1.00 marks the top of the healthy band, and the whole healthy range runs roughly 0.74–1.00 — a prime far below 1.00 means underweight, not optimal. The ponderal index (kg/m³) scales better at extreme heights.

Where BMI breaks down

BMI cannot see body composition: a linebacker and a sedentary person can share a “obese” score. It overestimates risk in tall, muscular, and pregnant people, and underestimates it in shorter people and older adults who lost height. Waist circumference adds the piece BMI misses — abdominal fat.

Worked example

A 5 ft 10 in (178 cm), 180 lb (81.6 kg) adult.
Metric conversion: 81.65 kg ÷ (1.78 m)².
1.78² = 3.168; 81.65 ÷ 3.168 = 25.8.
BMI 25.8 → just over the line into Overweight.

How to use it

Pick metric or imperial.
Enter weight and height (imperial height is total inches — 5 ft 10 in = 70).
Read the BMI, its category, and your healthy weight range.
Check the spectrum bar to see where you sit on the WHO scale.