The BMI Calculator computes your Body Mass Index — a widely used screening metric that estimates body fat based on your height and weight. It supports both metric (kg/cm) and imperial (lb/in) inputs and shows which WHO weight category you fall into.

How to Use This Calculator

1. Choose Metric (kg and cm) or Imperial (lbs and inches).
2. Enter your weight and height.
3. Optionally enter your age and gender for context.
4. Click Calculate BMI.

BMI Categories (WHO Standard)

• Below 18.5 — Underweight
• 18.5 – 24.9 — Normal / Healthy weight
• 25.0 – 29.9 — Overweight
• 30.0 and above — Obese (Class I: 30–34.9, Class II: 35–39.9, Class III: 40+)

Limitations of BMI

BMI is a quick screening tool, not a diagnostic. It has well-known limitations: athletes and muscular individuals often have a high BMI despite low body fat. Older adults may have a normal BMI with high body fat and low muscle. BMI also doesn’t account for where fat is stored — abdominal (visceral) fat is more dangerous than peripheral fat regardless of total BMI.

For a more complete picture, consider waist circumference (health risk increases above 35″ for women, 40″ for men) and waist-to-hip ratio alongside BMI.

Frequently Asked Questions

Is BMI accurate for children?

Adult BMI categories do not apply to children. For ages 2–19, BMI must be plotted on CDC growth charts and compared to same-age, same-sex percentiles. A pediatrician uses BMI-for-age, not the adult thresholds.

What BMI should I aim for?

For most adults, a BMI between 18.5 and 24.9 is associated with the lowest health risk. Research suggests that the lowest all-cause mortality is around 22–23 for women and 23–24 for men.

Does ethnicity affect BMI interpretation?

Yes. Asian populations have higher metabolic risk at lower BMI thresholds. The WHO recommends adjusted cut-points for Asian adults: overweight at BMI 23+, obese at BMI 27.5+.