Free Online BMI Calculator

BMI (Body Mass Index) measures body fat based on height and weight. The formula is weight in kilograms divided by height in meters squared (kg/m²). For example, a person who is 1.75 m tall and weighs 70 kg has a BMI of 22.9. In imperial units, multiply weight in pounds by 703, then divide by height in inches squared.

A BMI between 18.5 and 24.9 is considered normal weight by the World Health Organization. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. These ranges apply to adults aged 20 and older.

The WHO defines six categories: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40 and above). Each category indicates different levels of weight-related health risk.

The BMI formula is the same for men and women. However, women typically carry more body fat at the same BMI. The WHO categories apply equally to both sexes, but healthcare providers may interpret results differently based on individual factors.

BMI does not distinguish between muscle and fat, so athletes or highly muscular people may be classified as overweight despite low body fat. It also does not account for age, bone density, or fat distribution. BMI is a screening tool, not a definitive health diagnosis.

Multiply your weight in pounds by 703, then divide by your height in inches squared. For example: 160 lbs and 70 inches tall = (160 × 703) / (70 × 70) = 22.9 BMI.

A BMI of 30 or above is classified as obese. Obesity is further divided into three classes: Class I (30–34.9), Class II (35–39.9), and Class III (40 and above), also called severe or morbid obesity. Higher classes indicate greater health risk.

Standard BMI categories do not apply to children and teens. For ages 2–19, BMI is interpreted using age- and sex-specific percentiles called BMI-for-age. This calculator is designed for adults aged 20 and older.