Skip to content
BMICalc

BMI Calculator

Calculate your Body Mass Index instantly — free, private, no signup required.

  • Instant results as you type
  • Imperial & metric units
  • No data stored or shared
  • WHO-standard categories
ft
in
lbs
Note: BMI interpretation differs for children under 18. These results use adult BMI ranges (18.5–24.9 = healthy).

For informational purposes only. Consult a healthcare professional for medical advice.

BMI Categories

The World Health Organization defines these BMI ranges for adults aged 20 and older:

BMI Range Category
Below 18.5 Underweight
18.5 – 24.9 Normal weight
25.0 – 29.9 Overweight
30.0 – 34.9 Obese (Class I)
35.0 – 39.9 Obese (Class II)
40.0 and above Obese (Class III)

What Is BMI?

Body Mass Index (BMI) is a numerical value derived from a person's weight and height. It provides a simple, widely used indicator of whether an adult has a healthy body weight for their height.

BMI was developed in the early 19th century by Belgian mathematician Adolphe Quetelet and adopted by the World Health Organization as an international standard for recording obesity statistics. While it does not directly measure body fat, research has shown that BMI correlates reasonably well with body fat as measured by more direct techniques.

How Is BMI Calculated?

BMI is calculated using these formulas:

  • Metric: BMI = weight (kg) ÷ height² (m²)
  • Imperial: BMI = (weight (lbs) ÷ height² (in²)) × 703

For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 70 ÷ (1.75²) = 22.9 — in the Normal weight range.

Limitations of BMI

While BMI is a useful population-level screening tool, it has important limitations for individual health assessment:

  • Does not measure body fat directly. Athletes and muscular individuals may have a high BMI despite low body fat.
  • Varies by age, sex, and ethnicity. The same BMI may carry different health implications across populations. Lower cut-off points apply for some Asian populations.
  • Does not assess fat distribution. Abdominal (visceral) fat is a stronger predictor of metabolic risk than BMI alone. Waist circumference provides additional context.
  • Not suitable for children or adolescents. Use age- and sex-specific BMI-for-age percentile charts instead.
  • Not suitable during pregnancy or for individuals with certain medical conditions.

For a comprehensive assessment, your healthcare provider may also consider waist circumference, blood glucose, lipid panel, blood pressure, and other clinical indicators.

When to See a Doctor

Schedule a consultation with your healthcare provider if:

  • Your BMI is below 18.5 or 30 and above
  • You have experienced unexplained weight changes
  • You have a family history of obesity-related conditions such as type 2 diabetes or heart disease
  • You have concerns about your diet, weight, or overall health

Latest Articles

View all articles →