BMI Calculator
Body Mass Index with WHO category and your healthy-weight range.
Formula
About this calculator
Body Mass Index (BMI) is a quick screening number that relates your weight to your height. It is calculated by dividing your weight in kilograms by the square of your height in metres, and it places most adults into one of four World Health Organization categories: underweight, normal weight, overweight or obese. This calculator works in both metric (cm and kg) and imperial (feet, inches and pounds) units and shows exactly which category you fall into.
The value of BMI is its simplicity — with just two measurements you get an at-a-glance sense of whether your weight sits in the range associated with the lowest health risk for the general adult population. The WHO cut-offs are: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obese. Alongside your number, this tool also shows the healthy-weight range for your specific height, so you can see how many kilograms or pounds separate you from the normal band.
BMI has real limitations, and it is important to read the number in context. Because it uses only height and weight, it cannot tell muscle from fat — a very muscular athlete can register as overweight despite low body fat, while an older person who has lost muscle may look healthy on BMI while carrying excess fat. It also does not account for where fat is stored; abdominal fat carries more health risk than fat on the hips and thighs. Treat BMI as a starting point for a conversation with a healthcare professional, not a diagnosis.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared. In imperial units it is weight in pounds times 703, divided by height in inches squared — this calculator handles the conversion for you.
What is a healthy BMI range?
For most adults the World Health Organization considers a BMI of 18.5 to 24.9 to be the normal, healthy-weight range. Below 18.5 is underweight and 25 or above is overweight.
Is BMI accurate for athletes?
Not always. BMI cannot distinguish muscle from fat, so muscular people can score as overweight despite being lean. Body-composition measures like waist circumference or body-fat percentage give a fuller picture.
Does BMI work for children?
The adult categories used here do not apply to children and teenagers, whose BMI is assessed against age- and sex-specific percentile charts. Use a paediatric BMI-for-age tool instead.
Related calculators
⚠️ BMI is a general screening tool, not a diagnosis, and does not account for muscle mass, body composition or fat distribution. Consult a healthcare professional for personal advice.