Metric formula
BMI = kg ÷ m²
Divide your weight in kilograms by your height in metres squared.
Free adult BMI calculator
Check your BMI
Enter your height and weight for an instant body mass index result and an estimated healthy weight range.
Your result
22.9 BMI
Healthy weightYour position on the BMI scale
Estimated healthy weight range56.7–76.3 kg
Your result is within the healthy weight range for most adults.
BMI is a screening measure, not a diagnosis. Speak to a healthcare professional if you have concerns about your weight or health.
This calculator uses adult BMI categories and is intended for people aged 18 and over. It is not suitable during pregnancy.
The calculation
How BMI is worked out
Body mass index compares your weight with your height. It provides a quick starting point for understanding whether your weight may be affecting your health.
Imperial formula
BMI = lb ÷ in² × 703
Divide pounds by inches squared, then multiply the result by 703.
Your result in context
Understanding adult BMI
BMI categories are useful for population screening, but they do not tell the whole story about an individual’s health.
CategoryBMI range
UnderweightBelow 18.5
Healthy weight18.5–24.9
Overweight25.0–29.9
Obesity30.0 or above
BMI does not measure body fat directly
It cannot distinguish muscle from fat, so it may overestimate risk in people with a muscular build.
Where weight is carried matters
Waist measurement and other health indicators can provide useful context alongside BMI.
Children need a different assessment
For children and teenagers, BMI is interpreted by age and sex using growth-chart percentiles.
Common questions
About BMI calculators
Clear answers to the questions people most often ask about BMI.
What is a healthy BMI?
For most adults aged 18 and over, a BMI from 18.5 to 24.9 is classed as the healthy weight range. It is still important to consider other health information.
Is BMI accurate for everyone?
No single screening measure is perfect. BMI does not distinguish muscle from body fat or show where fat is carried, so it can be less informative for muscular people, during pregnancy and in some other circumstances.
Does BMI account for muscle?
No. Muscle and fat both contribute to body weight, so people with high muscle mass may have a higher BMI without having a high level of body fat.
Does age or sex change the adult calculation?
The standard adult formula and thresholds are the same for adult men and women. Age and sex are essential when interpreting BMI for children and teenagers, who need a percentile-based assessment.
Should I make health decisions from my BMI?
BMI is a starting point, not a diagnosis. A GP or other qualified healthcare professional can interpret it alongside your medical history, waist measurement and other relevant information.
Health information sources
Our calculator follows the standard adult BMI formula and category thresholds described by the NHS and US Centers for Disease Control and Prevention.
Information reviewed 23 September 2026.