Body mass index (BMI) is a screening measure that compares weight with height. For adults, it can be calculated using kilograms and metres or pounds and inches. BMI is useful as one health indicator, but it is not a diagnosis and does not directly measure body fat.
Quick answer: Adult BMI = weight in kilograms ÷ height in metres squared.
BMI formula in metric units
BMI = weight (kg) / [height (m) x height (m)]
For example, if an adult weighs 70 kg and is 1.75 m tall: 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = approximately 22.9.
BMI formula in US units
BMI = 703 x weight (lb) / [height (in) x height (in)]
Use total height in inches. For example, 5 feet 8 inches is 68 inches. Do not enter 5.8 as a height in inches.
Adult BMI categories
The US Centers for Disease Control and Prevention (CDC) lists the following screening categories for adults aged 20 and older:
| Category | BMI range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to below 25 |
| Overweight | 25 to below 30 |
| Obesity | 30 or higher |
These categories are adult screening ranges, not an individual diagnosis. See the CDC’s Adult BMI Categories and BMI Frequently Asked Questions for further context.
What BMI cannot tell you
BMI does not directly measure body fat, muscle mass, fat distribution, fitness, or overall health. Two people with the same BMI can have different body compositions and health profiles. A healthcare professional may consider other information, including physical examination, medical history, blood pressure, and laboratory results.
Adult BMI ranges should not be used to interpret children and teenagers. For ages 2 through 19, BMI is interpreted using age- and sex-specific percentiles. Pregnancy and certain athletic or medical circumstances also require individual interpretation.
Calculate BMI online
Use the Calclio BMI Calculator to estimate BMI from height and weight. Check that the selected unit system matches the values you enter.
Frequently asked questions
Is BMI 22.9 healthy?
For adults aged 20 and older, 22.9 falls within the CDC’s healthy-weight screening range. It does not by itself prove that a person is healthy.
Does BMI change with age?
The adult screening categories are generally applied to adults 20 and older, but health interpretation still depends on the individual. Children and teenagers use a different percentile method.
Can BMI be used for children?
Children and teens need age- and sex-specific BMI percentiles rather than the adult category table. Ask a qualified healthcare professional about an individual child’s result.
Health information only. Calclio does not provide medical diagnosis or treatment. Discuss health questions with a qualified healthcare professional.