BMI Calculator

Choose metric or imperial measurements.

Select the standard adult categories or the lower NICE thresholds.

Enter height and weight. The result shows BMI, the corresponding screening category, and the height-based reference-weight interval.

The calculator is intended for adults aged 20 and older.

Body mass index compares weight with height by dividing weight in kilograms by height in metres squared.

BMI is a quick screening measure of weight relative to height.

It does not directly measure body fat, distinguish fat from muscle and bone, or show where body fat is carried.

Standard adult categories classify BMI below 18.5 as underweight, 18.5 to below 25 as healthy weight, 25 to below 30 as overweight, and 30 or higher as obesity.

Obesity is divided into class 1 from 30 to below 35, class 2 from 35 to below 40, and class 3 from 40 upward.

These are screening categories rather than diagnoses or judgements about an individual.

NICE recommends lower practical thresholds for adults from South Asian, Chinese, other Asian, Middle Eastern, Black African, or African-Caribbean backgrounds because cardiometabolic risk can occur at a lower BMI.

Under this interpretation, overweight begins at BMI 23 and obesity begins at BMI 27.5.

The higher obesity-class boundaries are usually reduced by 2.5 BMI points.

The height-and-weight formula remains exactly the same. Only the category interpretation changes.

The calculator multiplies the lower and upper healthy-BMI boundaries by height in metres squared.

This shows the weights that correspond mathematically to the selected healthy-BMI interval at the entered height.

It is not an ideal weight, required goal, medical recommendation, or treatment target.

BMI should be considered with medical history, physical examination, blood pressure, laboratory findings, activity, body composition, and other relevant information.

It may be less informative for people with high muscle mass, unusual body composition, conditions affecting height, or complex health needs.

Children and teenagers require BMI-for-age assessment rather than adult thresholds.

The calculator displays BMI to one decimal place and applies the category thresholds to that displayed result.

Small measurement differences near a boundary can therefore change the displayed category.

Height and weight measurements themselves also contain uncertainty, so a category boundary should not be interpreted as a precise biological dividing line.

The BMI calculation runs entirely in the browser.

Height, weight, selected thresholds, and results are not uploaded, added to a public URL, or permanently stored.