BMI Calculator
Calculate your Body Mass Index (BMI) using US, metric, or any other combination of height and weight units, with a visual gauge and healthy weight range.
Understanding BMI
Body Mass Index (BMI) is a simple screening measure calculated from height and weight: BMI = weight (kg) / height (m)². It doesn't measure body fat directly, but for most adults it correlates reasonably well with it, which is why it's widely used as a quick, inexpensive first check of whether someone's weight falls into a healthy range for their height.
BMI Prime is your BMI divided by 25 (the upper bound of the normal range), so a BMI Prime of 1.0 means you're exactly at that boundary — values below 1.0 fall within or under the normal range. The Ponderal Index is a similar but less common measure that uses height cubed instead of squared (weight (kg) / height (m)³), which makes it more accurate than BMI for people who are unusually tall or short.
BMI doesn't distinguish between muscle and fat, so very muscular people can show a high BMI without carrying excess body fat, and it doesn't account for where fat is distributed, which also affects health risk. It's also less reliable for children, teens, pregnant women, and older adults, whose healthy ranges differ from the standard adult categories used here. BMI is best treated as a starting point, not a diagnosis — a doctor can interpret it alongside other measurements like waist circumference or body fat percentage.
Frequently Asked Questions
About this calculator
This BMI calculator computes Body Mass Index from height and weight, with full support for US units, metric units, or any custom combination of units you prefer — including pounds, kilograms, stone, feet, inches, and centimeters. Results include a visual gauge showing where your BMI falls, your healthy weight range for your height, and two related figures: BMI Prime and the Ponderal Index.
- Three unit systems — Switch between US units (feet/inches, pounds), metric units (cm, kg), or mix and match any height and weight unit — including stone, ounces, and grams.
- Visual BMI gauge — A color-coded gauge shows exactly where your BMI falls across the underweight, normal, overweight, and obese ranges.
- Healthy weight range — Shows the specific weight range — in your chosen unit — that corresponds to a normal BMI for your exact height.
- BMI Prime & Ponderal Index — Two related measures: BMI Prime (your BMI relative to the upper normal limit) and the Ponderal Index, a height-cubed alternative to BMI that's more accurate for unusually tall or short people.
- Child & teen notice — Flags when age-based BMI percentile charts, rather than standard adult ranges, are the more appropriate way to assess weight status.