Free tool · runs in your browser
BMI Calculator: Adult Body Mass Index and Categories
Calculate adult BMI in US or metric units. See CDC screening categories, a worked example, measurement tips and what the number can and cannot tell you.
The short answer: BMI is weight in kilograms divided by height in meters squared. Enter adult height and weight to calculate the number and see the CDC screening category. Adult categories apply from age 20; this is not a diagnosis or a calorie target.
How to calculate BMI
For metric measurements, BMI = weight in kilograms ÷ (height in meters × height in meters). At 70 kg and 1.75 m, the calculation is 70 ÷ 3.0625 = 22.86, displayed as 22.9. The category uses the unrounded number, so rounding cannot move a result across a threshold.
For US measurements, this tool converts pounds to kilograms and inches to meters before applying the same formula. Enter total inches: 5 feet 9 inches is 69 inches. Changing units carries the measurements across; it does not reinterpret 175 centimeters as 175 inches.
Adult BMI categories
The CDC adult categories use the following cutoffs for people 20 and older.
| BMI | Screening category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Healthy weight |
| 25 to below 30 | Overweight |
| 30 or higher | Obesity |
What the result can and cannot tell you
The CDC adult calculator describes BMI as one health indicator to consider with medical history, examination and other findings. BMI relates weight to height; it does not directly measure body fat, muscle or where fat is distributed. A screening category does not by itself establish a person's health.
Use the result as information for a conversation with a qualified clinician, rather than a reason to select a restrictive diet. This adult tool is not intended for children or teenagers, and pregnancy requires a different clinical interpretation. A child's BMI uses age- and sex-specific growth references rather than this adult category table.
Check the inputs before comparing results
Use the same units and a current height measurement each time. Remove an accidental extra zero and check whether weight was entered in pounds or kilograms. If two calculators disagree slightly, compare the precision of the measurements and whether they round before assigning a category. A tiny difference near a cutoff is a reason to discuss context, not to chase a particular decimal.
Measurements entered here are processed in this page's browser script; the calculator does not submit or save the fields. You can write down the result if you want to discuss it at an appointment.
Questions, answered
How is BMI calculated? BMI is weight in kilograms divided by height in meters squared. This calculator converts US measurements to metric before calculating, then displays one decimal place. The category is assigned using the unrounded result.
What is a healthy adult BMI range? The CDC adult healthy-weight BMI category runs from 18.5 to less than 25 for adults 20 and older. BMI is a screening measure and should be interpreted alongside other health information.
Can I use this BMI calculator for a child? This BMI calculator is for adults 20 and older. Children and teenagers need an age- and sex-specific BMI assessment, so use the CDC child and teen resource or speak with a clinician.