Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = weight (kg) ÷ height (m)². It's used as a screening tool to categorize weight status.

What BMI is considered healthy?

For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight range, according to the World Health Organization and CDC. Below 18.5 is underweight, 25–29.9 is overweight, and 30+ is classified as obesity.

Is BMI accurate for everyone?

BMI is a useful population-level screening tool but has known limitations. It doesn't distinguish between muscle and fat, so athletes and very muscular individuals may show a high BMI despite low body fat. It also doesn't account for age, sex, or fat distribution.

Does BMI apply to children?

No. This calculator is designed for adults aged 20 and over. Children and teens require age- and sex-specific BMI percentile charts, since their body composition changes as they grow.

How is the healthy weight range calculated?

We calculate the weight that would produce a BMI of 18.5 and a BMI of 24.9 at your entered height, giving you a personalized healthy weight window in kilograms or pounds.

What should I do if my BMI is outside the healthy range?

A BMI outside 18.5–24.9 doesn't automatically indicate a health problem. Consult a healthcare provider for a full assessment that considers body composition, waist circumference, diet, activity level, and family history.

What's the difference between metric and imperial BMI formulas?

The underlying formula is the same. In metric units it's weight (kg) ÷ height (m)². In imperial units, the equivalent formula is 703 × weight (lb) ÷ height (in)². Our calculator converts imperial inputs to metric internally for consistency.

Can I use BMI to track fat loss progress?

BMI can be one data point among many, but because it doesn't measure body fat directly, it's better paired with other metrics like waist circumference, body fat percentage, or progress photos for tracking fat loss.

Is a low BMI always healthy?

Not necessarily. A BMI under 18.5 can be associated with nutritional deficiencies, reduced bone density, or a weakened immune system, and should be discussed with a healthcare provider.

How often should I check my BMI?

There's no strict rule, but checking every few months alongside other health metrics is reasonable for most people monitoring general health trends.

BMI Calculator

Calculate your Body Mass Index and see your healthy weight range, in metric or imperial units.

Height (cm)

Weight (kg)

Your BMI

24.2

Healthy weight

Healthy weight range

53.5 kg – 72.0 kg

How to use the BMI calculator

1
Select metric (centimeters and kilograms) or imperial (feet, inches, and pounds) units.
2
Enter your current height and weight.
3
Your BMI score, weight category, and healthy weight range update instantly.

The BMI formula explained

Body Mass Index was developed in the 1830s by Belgian mathematician Adolphe Quetelet as a simple way to describe relative weight across large populations. It has since become the standard screening metric used by the World Health Organization, the CDC, and physicians worldwide.

Metric formula: BMI = weight in kilograms ÷ (height in meters)²

Imperial formula: BMI = 703 × weight in pounds ÷ (height in inches)²

Example (metric): A person who weighs 70 kg and is 1.70 m tall has a BMI of 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 = 24.2, which falls in the healthy weight category.

Example (imperial): A person who weighs 154 lb and is 5'7" (67 inches) tall has a BMI of 703 × 154 ÷ (67 × 67) = 108,262 ÷ 4,489 = 24.1 — essentially identical to the metric example above, confirming the two formulas are mathematically equivalent.

BMI range	Category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 and above	Obesity

Limitations of BMI

While BMI is fast and free to calculate, it has well-documented limitations. Because it only considers height and total body weight, it cannot distinguish between muscle mass, bone density, and fat mass. A bodybuilder and a sedentary person of the same height and weight will have identical BMI scores despite very different body compositions and health risk profiles.

BMI thresholds also don't adjust for age, sex, or ethnicity, even though research shows body fat distribution and associated health risks can vary across these groups at the same BMI value. For a more complete picture, healthcare providers often combine BMI with waist circumference, waist-to-hip ratio, or direct body composition measurements like DEXA scans or bioelectrical impedance analysis.

Despite these caveats, BMI remains valuable precisely because it's quick, free, and requires no special equipment — making it an effective first-pass screening tool for population health studies and a useful personal benchmark to track over time.