BMI Calculator
Calculate your Body Mass Index and find your healthy weight range.
By Syed Mubashir Ali · Last updated
For general information only — not medical advice. If you have a health concern, speak to a qualified professional.
How to Use BMI Calculator
- 1Select your preferred unit system: Metric (kg/cm) or Imperial (lbs/ft/in).
- 2Enter your weight in the weight field.
- 3Enter your height in the height field.
- 4For a child or teenager, enter their age in years and months and choose boy or girl. Leave the age blank for an adult.
- 5Your BMI, weight category, and healthy weight range are calculated instantly. Adults also see BMI Prime and the Ponderal Index; under 20, the BMI-for-age percentile from CDC's growth charts.
- 6Reference the category chart at the bottom to understand what your BMI means.
Frequently Asked Questions
What is BMI?
BMI (Body Mass Index) is a numerical value calculated from a person's weight and height. It's used as a screening tool to indicate whether a person may be underweight, normal weight, overweight, or obese.
How is BMI calculated?
BMI = weight (kg) ÷ height² (m²). For imperial units, BMI = 703 × weight (lbs) ÷ height² (inches²). The same categories apply regardless of which unit system is used.
Is BMI an accurate measure of health?
BMI is a useful population-level screening tool, but it has limitations. It doesn't distinguish between muscle and fat mass: athletes may have high BMIs due to muscle. It also doesn't account for age, sex, ethnicity, or body fat distribution. Always consult a healthcare provider for a comprehensive health assessment.
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is classified as 'Normal weight' for most adults. Below 18.5 is underweight. 25–29.9 is overweight. 30 and above is classified as obese (with further classes above 35 and 40).
Can I use it for a child or teenager?
Yes: enter their age and choose boy or girl. Under 20 the adult bands don't apply, because a healthy BMI changes with age and differs between boys and girls. The calculator places the BMI as a percentile on the CDC 2000 BMI-for-age growth charts and uses CDC's categories: below the 5th percentile is underweight, 5th to 85th healthy, 85th to 95th overweight, and 95th or above obesity. CDC's own example: a 12-year-old girl who is 5 ft tall and weighs 136 lb has a BMI of 26.6, only 'overweight' by adult bands, but at the 96th percentile for her age, which is obesity. The charts start at age 2.
What are BMI Prime and the Ponderal Index?
BMI Prime is your BMI divided by 25, the top of the healthy range, so 1.00 is the limit and 1.20 means 20% over it. The Ponderal Index divides weight by height cubed rather than squared, so it is less skewed for very tall or very short people. Both are shown for adults.
About BMI Calculator
The BMI Calculator is a quick, free tool for estimating your body mass index: a widely used indicator of whether your weight falls within a healthy range for your height. While not a diagnostic tool, BMI calculations are routinely used in clinical settings as a first-pass screening for weight-related health risks.
The calculator supports both metric (kilograms and centimeters) and imperial (pounds, feet, and inches) input, making it accessible to users worldwide. It instantly computes your BMI, identifies your weight category, and shows the healthy weight range specific to your height: giving you a concrete target if you're looking to reach or maintain a healthy weight.
The six BMI categories follow the World Health Organization classifications: 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). The color-coded scale provides an at-a-glance view of where your BMI falls relative to all categories.
It's important to note that BMI is a screening tool, not a diagnostic measure. Factors like age, muscle mass, bone density, and ethnicity can affect the interpretation of BMI. For example, athletes and bodybuilders often have high BMIs due to muscle mass rather than excess fat. Children and teenagers are compared with others of the same age and sex on growth charts rather than with the adult bands, which the calculator does when you enter an age under 20. Always discuss your results with a qualified healthcare provider.