BMI Calculator
Calculate your Body Mass Index using metric (kg / cm) or imperial (lbs / ft·in) units. Your result includes your BMI value and the corresponding WHO weight category.
Notes
What Is BMI?
Body Mass Index (BMI) is a number calculated from your weight and height. It is used worldwide as a simple screening tool to classify adults into weight categories — underweight, normal, overweight, or obese.
BMI Formula
For imperial measurements, the formula uses a conversion factor:
BMI Categories (WHO)
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese — Class I | 30.0 – 34.9 |
| Obese — Class II | 35.0 – 39.9 |
| Obese — Class III | 40.0 and above |
Limitations of BMI
- Does not distinguish between muscle mass and fat mass — athletes may be classified as overweight despite low body fat.
- Does not account for age, sex, or ethnicity differences in body composition.
- May underestimate health risks in people with low muscle mass (e.g., elderly individuals).
- Does not indicate where fat is distributed on the body.
- BMI Formula – Variables & Derivation — Full formula breakdown with worked examples
- How to Calculate BMI – Step-by-Step Guide — Detailed explanation with worked examples
Frequently Asked Questions
What is a healthy BMI for adults?
The World Health Organization considers a BMI between 18.5 and 24.9 to be the normal weight range for adults. However, individual health also depends on age, muscle mass, and other factors.
How does this calculator handle imperial units?
When you select imperial, enter weight in pounds and height in feet and inches. The calculator applies the formula BMI = 703 × weight(lbs) / height(in)² automatically.
Is BMI the same for men and women?
The BMI formula and WHO category thresholds are the same for both men and women. However, men and women tend to differ in body fat percentage at the same BMI, which is one of BMI's known limitations.
Does BMI apply to children?
Adult BMI categories do not apply to children. For those under 18, BMI-for-age percentile charts (from the WHO or CDC) should be used instead.