BMI Calculator

--BMI Score
--Category
UnderweightNormalOverweightObese
1618.5253040+

BMI Reference Table

BMI RangeCategory
< 18.5Underweight
18.5 – 24.9Normal weight
25 – 29.9Overweight
30 – 34.9Obese (Class I)
35 – 39.9Obese (Class II)
≥ 40Obese (Class III)

What Is BMI and How Is It Calculated?

Body Mass Index (BMI) is a numerical value derived from a person's height and weight. It provides a simple, quick screening tool to categorise individuals into weight status groups. The formula is: BMI = weight (kg) / height (m)². For imperial measurements, the formula is BMI = (weight in lbs × 703) / (height in inches)².

BMI Categories Explained

The World Health Organization (WHO) defines four primary BMI categories for adults:

  • Underweight (BMI < 18.5): May indicate malnutrition, eating disorders, or other health issues.
  • Normal weight (BMI 18.5–24.9): Associated with the lowest risk of weight-related chronic diseases.
  • Overweight (BMI 25–29.9): Increased risk for conditions like type 2 diabetes and hypertension.
  • Obese (BMI ≥ 30): Further divided into Class I, II, and III with progressively higher health risks.

Limitations of BMI

BMI is a population-level screening tool, not a clinical diagnostic measure. It does not directly measure body fat or account for muscle mass, bone density, age, or sex differences in fat distribution. Athletes with high muscle mass may have an elevated BMI without excess fat. Conversely, elderly individuals can have a "normal" BMI while having unhealthy levels of body fat.

Tips for Achieving a Healthy BMI

Maintaining a BMI in the normal range generally involves a balanced diet rich in whole foods, regular physical activity (at least 150 minutes of moderate exercise per week), adequate sleep, and stress management. Small, consistent lifestyle changes are more sustainable than crash diets.

Frequently Asked Questions

Is BMI accurate for everyone?
BMI is a useful population-level screening tool but has limitations for individuals. It may overestimate body fat in muscular people and underestimate it in those who have lost muscle mass. Always consult a healthcare provider for a comprehensive health assessment.
What BMI is considered healthy?
A BMI between 18.5 and 24.9 is considered the normal or healthy weight range for adults according to the World Health Organization.
Does BMI differ for men and women?
The standard BMI calculation uses the same formula for both sexes. However, women naturally carry more body fat than men at the same BMI, so some researchers suggest gender-specific cut-offs for more accurate health assessments.
How often should I calculate my BMI?
Checking your BMI every few months is usually sufficient to track long-term trends. Daily or weekly fluctuations in weight are mostly water weight and not meaningful for BMI assessment.
Can children use this BMI calculator?
No. This calculator is designed for adults (18+). Children and teens require age- and sex-specific BMI percentile charts because body fat changes significantly during growth.