BMI Calculator

Body mass index, usually called BMI, is a weight-to-height estimate used to place an adult result into broad weight-status categories. It is quick to calculate because it only needs weight and height.

BMI is best treated as a screening estimate. It can help start a conversation about weight range, but it is not a diagnosis and it does not measure body fat directly.

1. Choose Metric Units, US Units, or Other Units.
2. Enter age if you want the child/teen warning to be applied.
3. Select gender if useful for your records. It does not change BMI.
4. Enter height and weight, then choose Calculate.
5. Review BMI, category, healthy range, and the notes below the result.

NexaCalc uses the standard adult BMI formula after converting all inputs to kilograms and meters.

Pounds are converted to kilograms with 1 lb = 0.45359237 kg. Feet and inches are converted to meters using 1 inch = 2.54 cm.

For a person who weighs 70 kg and is 175 cm tall, height is 1.75 m. The calculation is 70 / (1.75 x 1.75), which gives a BMI of 22.9. That result falls in the normal weight category for adults.

The healthy weight range shown in the result is calculated from the adult BMI range of 18.5 to 24.9 for the height you entered.

This range is a mathematical BMI range, not a personalized target. Health history, body composition, and clinician guidance can change what is appropriate for an individual.

BMI Prime compares your BMI with 25, the adult cutoff where the overweight category begins in this calculator. A BMI Prime of 1.00 means BMI is exactly 25. Values below 1 are below 25, and values above 1 are above 25.

Ponderal Index is another height-adjusted body-size measure. It uses weight in kilograms divided by height in meters cubed. Because it scales height differently than BMI, it can give a second perspective for very short or very tall adults, but it is still only an estimate.

Adults and children are interpreted differently. For people below age 20, BMI is usually evaluated with BMI-for-age percentiles that compare children or teens with others of the same age and sex.

This calculator can still compute the adult BMI formula, but the result should not be used as a child growth assessment.

BMI does not distinguish muscle, fat, bone, or fluid. Athletes, older adults, pregnant people, and people with different body composition patterns may have BMI results that do not reflect their actual health risk.

Treat BMI as a general screening estimate. For medical decisions, combine it with professional advice and other measurements.

BMI uses only height and weight. Body fat percentage tries to estimate how much of total body weight is fat. That usually needs additional measurements, devices, or clinical methods.

BMI is simpler and faster, while body fat percentage can be more specific when measured carefully. The two numbers answer related but different questions.

• CDC Adult BMI Categories: adult BMI ranges, screening context, and adult interpretation.
• CDC Child and Teen BMI Categories: BMI-for-age percentile approach for ages 2 through 19.
• WHO Obesity and Overweight Fact Sheet: international public-health context for BMI and weight status.