Free tool
Body mass index from kilograms and centimeters or from pounds, feet and inches, with the formula worked out and the CDC adult category. For adults 20 and older; children and teens use BMI-for-age percentiles instead.
Built for NHA CCMA exam prepMetric: weight in kilograms divided by height in meters squared. US: pounds divided by inches squared, times 703.
Enter a height and a weight.
BMI math, the CDC categories, the 703 factor and the unit conversions around it are all cards in the free NHA CCMA course.
Get started freeBody mass index is weight (kg) / height (m)2. In US units it is
weight (lb) / height (in)2 x 703; the 703 converts pounds and inches to the metric result, and a
pounds-over-feet version with no factor is simply wrong. Convert feet to inches first (1 foot is 12 inches) and note that
1 inch is exactly 2.54 cm and 1 kg is about 2.2 lb.
Worked examples: 70 kg and 1.75 m is 70 / (1.75 x 1.75) = 70 / 3.0625 = 22.9, a healthy weight. 180 lb and 70 inches is 180 x 703 = 126,540, divided by 70 x 70 = 4,900, which gives 25.8, overweight.
| CDC adult category (20 and older) | BMI |
|---|---|
| Underweight | below 18.5 |
| Healthy weight | 18.5 to below 25 |
| Overweight | 25 to below 30 |
| Obesity, class 1 | 30 to below 35 |
| Obesity, class 2 | 35 to below 40 |
| Obesity, class 3 (severe) | 40 or greater |
The adult categories apply to adults 20 and older regardless of age, sex or race. BMI is a screening measure, not a diagnosis: muscle is denser than fat and fat distribution varies, so it is read with other findings such as waist circumference. Children and teens aged 2 through 19 are classified by BMI-for-age percentile on a growth chart instead (underweight below the 5th percentile, healthy 5th to below 85th, overweight 85th to below 95th, obesity at or above the 95th), and BMI is not used under age 2. The explainer is the BMI formula and categories; height, weight and growth charts are in the intake unit of the free NHA CCMA course.
This tool is a study aid for the CCMA exam, not clinical guidance. Real care follows the provider's orders and your facility's protocols.
The BMI formula in metric and imperial units (weight in pounds times 703), the CDC adult categories and obesity classes, worked examples and the limits of BMI.
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