BMI Calculator

How to use

1. Choose Units — Select metric (kg/cm) or imperial (lbs/ft-in)
2. Enter Measurements — Input your weight and height
3. See Result — View your BMI score and weight category

What Is BMI?

Body Mass Index (BMI) is a numerical value calculated from a person's weight and height. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is widely used by healthcare professionals as a quick screening tool for weight categories that may lead to health problems.

The formula is simple: BMI = weight (kg) ÷ height (m)². For imperial units: BMI = weight (lbs) × 703 ÷ height (inches)². Despite its simplicity, BMI provides a useful population-level indicator of weight status.

BMI Categories (WHO Classification)

• Underweight: BMI below 18.5 — may indicate malnutrition, eating disorders, or other health conditions
• Normal weight: BMI 18.5 to 24.9 — associated with the lowest health risks from weight-related conditions
• Overweight: BMI 25.0 to 29.9 — increased risk for cardiovascular disease, diabetes, and hypertension
• Obese: BMI 30.0 and above — significantly elevated health risks; further subdivided into Class I (30-34.9), Class II (35-39.9), and Class III (40+)

Limitations of BMI

BMI is a useful screening tool but has important limitations:

• Doesn't measure body fat directly: A muscular athlete and a sedentary person of the same height and weight will have the same BMI
• No age consideration: Older adults tend to have more body fat than younger adults at the same BMI
• No sex differences: Women typically have more body fat than men at the same BMI
• No fat distribution: Abdominal fat (visceral fat) is more dangerous than fat stored elsewhere, but BMI doesn't account for this

When to Use BMI

BMI is most useful as a starting point for health discussions with your doctor. It works well for population-level studies and general screening but should be supplemented with other measurements like waist circumference, body fat percentage, and clinical assessments for individual health decisions.

Privacy

All calculations run entirely in your browser. Your weight and height data are never sent to any server or stored anywhere.

Track your health metrics with our Age Calculator. Calculate percentages with our Percentage Calculator.

Frequently asked questions

What is BMI?

Body Mass Index (BMI) is a simple measure of body fat based on weight and height. It's calculated as weight (kg) divided by height (m) squared. It's used as a screening tool, not a diagnostic measure.

What is a healthy BMI range?

A BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25-29.9 is overweight, and 30+ is obese according to WHO classifications.

Is BMI accurate for everyone?

BMI doesn't distinguish between muscle and fat mass. Athletes with high muscle mass may have a high BMI without being overweight. It also doesn't account for age, sex, bone structure, or fat distribution.

Should I rely solely on BMI?

No. BMI is a screening tool, not a diagnosis. Consult a healthcare professional for a complete health assessment that considers waist circumference, body composition, and other factors.

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