BMI Calculator

Body mass index (BMI) is an internationally used indicator that assesses obesity using weight and height. It lets you estimate body type without directly measuring body fat.

Enter only your weight (kg) and height (cm) to see your BMI along with a classification of underweight, normal, overweight, or obese.

For example, a person weighing 65 kg and 170 cm tall has a BMI of about 22.5, which is in the normal range.

BMI Calculator Calculation Method

Criteria: under 18.5 underweight, 18.5–23 normal, 23–25 overweight, 25+ obese

BMI: 0

Assessment:

About This Calculator

Body mass index (BMI) is a simple ratio of weight to height squared, used by the WHO and most health services as a first-pass screen for underweight, healthy weight, overweight and obesity.

Enter your weight and height — metric or imperial — to get your BMI and its weight category.

BMI is weight in kilograms divided by height in metres squared, with 18.5–24.9 treated as normal, 25–29.9 as overweight and 30 or above as obese. It is a population screening tool, not a diagnosis: a 180 cm athlete weighing 90 kg scores 27.8 with little body fat, while an older adult with low muscle can score 23 and still carry excess fat.

Key Formula:BMI = weight (kg) / height (m)²

Frequently Asked Questions

What is a healthy BMI range?

The WHO classifies 18.5–24.9 as healthy, below 18.5 as underweight, 25–29.9 as overweight and 30 or above as obese. Some countries use lower thresholds for Asian populations.

What are the limitations of BMI?

BMI ignores body composition, so muscular athletes can be classed as overweight and older adults can carry excess fat at a "normal" BMI. It is a population screen, not a personal diagnosis — waist circumference and body-fat percentage add context.

Is BMI different for children?

Yes. For under-20s, BMI is plotted on age- and sex-specific growth charts and expressed as a percentile, because body composition changes rapidly during growth.

Does BMI work the same way for children?

No. Children and adolescents are assessed against age- and sex-specific percentile charts, where the 85th percentile marks overweight and the 95th obesity. Adult cut-offs would misclassify most teenagers.

What are the limits of BMI?

It cannot separate muscle from fat, ignores where fat sits — waist circumference predicts metabolic risk better — and was derived from European populations, so Asian guidelines set the overweight threshold at 23 instead of 25.

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Sources & last update

2026-10-19