How to Calculate BMI: kg/cm, Pounds and Adult Categories

 

Body mass index, or BMI, is a ratio calculated from weight and height. It can be used as one screening measure, but it does not diagnose a medical condition or directly measure body fat. Understanding the units, the adult age range and the limits of the categories matters more than treating the result as a complete health score.

The Adult BMI Calculator accepts kilograms and centimeters or pounds, feet and inches. It uses standard adult categories for people aged 20 and older. It does not prescribe a target weight, calorie intake or weight-loss plan.

Calculate BMI using kilograms and centimeters

The formula is BMI = weight in kilograms / height in meters squared. First divide centimeters by 100 to convert height to meters. Then multiply that height by itself and divide the weight by the result. The unit is kilograms per square meter, written kg/m².

For example, a weight of 70 kg and a height of 175 cm become 70 / (1.75 x 1.75). The result is approximately 22.8571, displayed as 22.86. Dividing directly by 175 squared would be incorrect because the formula requires meters, not centimeters.

Use pounds, feet and inches

Enter whole feet and additional inches separately. A height of 5 feet 10 inches is 5 x 12 + 10 = 70 inches. Additional inches should be at least zero and less than twelve; enter 6 feet 0 inches rather than 5 feet 12 inches.

The calculator converts pounds to kilograms using 1 lb = 0.45359237 kg, and inches to centimeters using 1 inch = 2.54 cm. It then applies the same metric BMI formula. For 150 lb and 5 feet 10 inches, the displayed result is 21.52.

You may also see the shortcut BMI = 703 x weight in pounds / height in inches squared. The factor 703 is rounded. Exact conversions can therefore give a slightly different number, especially when comparing results near a category boundary.

Understand standard adult categories

The CDC adult categories describe BMI below 18.5 as underweight, 18.5 to less than 25 as healthy weight, and 25 to less than 30 as overweight. A BMI of 30 or above falls within the obesity category, subdivided into Class 1 from 30 to less than 35, Class 2 from 35 to less than 40, and Class 3 from 40 upward.

These are screening categories, not a complete assessment of an individual. The calculator assigns a category using the unrounded value and displays the number to two decimal places. A result extremely close to a cutoff may round to the cutoff while still belonging to the category below it.

Why the age field does not change the formula

For this adult calculator, age confirms that the user is within its stated scope. It is not a multiplier or correction added to the formula. Standard adult BMI calculation also does not require sex. Two adults with the same measured height and weight receive the same BMI.

Children and teenagers require a separate approach using age- and sex-specific growth references. Do not apply this adult category table to someone under 20. The tool also does not assess pregnancy-related weight changes or nutritional needs for special medical circumstances.

Know what the number leaves out

BMI cannot distinguish muscle from fat or describe fat distribution. A muscular person can have a higher BMI without the same body composition as another person at that BMI. Individual interpretation can also depend on age, ancestry, medical history and other measurements.

Measure carefully, use the correct units and discuss an unexpected or concerning result with a qualified health professional. This calculator performs arithmetic on your entries; it cannot establish your health status. Its input limits are software limits, not recommended body sizes.

Sources and privacy

For category definitions and context, see CDC Adult BMI Categories and CDC About Body Mass Index. Calculations happen in your browser, and this calculator does not save or transmit the entered measurements. The hosting website may separately use analytics or other services under its own privacy practices.