BMI Calculator
Adult screening information, not medical advice or a diagnosis. BMI and waist measurements cannot determine your overall health or replace an individual assessment.
What does BMI measure?
Body mass index compares weight with height: divide weight in kilograms by height in metres squared. At 70 kg and 175 cm, BMI is approximately 22.86. Imperial measurements are converted using 2.54 cm per inch and 0.45359237 kg per pound.
BMI is a practical screening measure, not a direct measurement of body fat. It cannot distinguish muscle, bone and fat, or explain the cause of a weight change. Adult thresholds must not be applied to children or teenagers.
A reference range, not an ideal weight
The standard adult reference range runs from BMI 18.5 up to, but not including, 25. Multiplying those boundaries by height in metres squared gives a corresponding weight band. The displayed weights are approximate because they are rounded.
That band is not a prescribed target or a promise of good health. Clinical interpretation can differ with ethnic background, muscle mass, age and health conditions. A professional assessment may use different thresholds and priorities.
Why add a waist measurement?
Waist-to-height ratio is waist circumference divided by height, in the same units. It adds information about fat carried around the waist that BMI alone cannot provide. A ratio of 0.5 means the waist measures half the height.
NICE uses a reference band of 0.4 to below 0.5, an increased-risk band of 0.5 to below 0.6, and a higher-risk band from 0.6. These adult bands apply when BMI is below 35, across sexes and ethnic backgrounds. Ratios below 0.4 are not treated as progressively healthier.
When another assessment is needed
This calculator is for adults aged 18 and over. Do not use it during pregnancy, with a diagnosed or suspected eating disorder, or with a condition that affects height. Seek appropriate guidance from a healthcare professional instead.
Measurements stay in this page's memory. The calculator does not upload them, put them in links, store them in an account or save them in browser storage. Normal site navigation and visitor analytics still apply.
BMI calculator questions
The standard adult reference range is 18.5 to below 25. It is a screening range, not an individual diagnosis. Ethnic background, muscle mass, age and health conditions can change how a result should be interpreted.