BMI calculator
Body mass index in metric or imperial units with the WHO adult categories and the weight range for a normal BMI.
Your BMI
Body mass index is weight in kilograms divided by height in metres squared. In imperial units the same figure is 703 × weight in pounds ÷ height in inches squared. Enter your height and weight in either system; the result shows the index, the WHO category and the weight range that would put you between 18.5 and 24.9 at your height.
The World Health Organization classifies adult BMI as underweight below 18.5, normal from 18.5 to 24.9, overweight from 25 to 29.9 and obese at 30 and above, with obesity classes I, II and III at 30, 35 and 40. These cut-offs are the same for men and women.
BMI is a screening tool for populations, not a diagnosis. It cannot tell muscle from fat, so a muscular athlete can be "overweight" with very little body fat, and an older adult with low muscle mass can have a normal BMI and excess fat. It does not apply to children and adolescents, whose growth charts use age- and sex-specific percentiles, nor to pregnant women. Some health bodies use lower action thresholds for people of South Asian and East Asian descent.
How to use it
- Choose metric or imperial units.
- Enter your height (cm, or feet and inches) and weight (kg or lb).
- Read the BMI, the WHO category and the weight range for a normal BMI at your height.
- Use the result as a prompt for a conversation with a clinician, not as a verdict.
Frequently asked questions
What is a healthy BMI?
For adults, WHO defines the normal range as 18.5 to 24.9. The result table converts that to a weight range for your height so you can see how far you are from the band.
Why is BMI wrong for athletes?
Muscle is denser than fat. A rugby player at 100 kg and 1.85 m has a BMI of 29, "overweight", with a body-fat percentage that may be lower than that of a sedentary person with a normal BMI. Waist circumference or body-fat measurement is more informative in that case.
Can I use this for my child?
No. For ages 2 to 19 BMI is interpreted against age- and sex-specific percentile charts (WHO growth references or national charts), not the adult cut-offs shown here.
Are the cut-offs different for Asian populations?
WHO keeps the international cut-offs but notes that risk in many Asian populations rises at lower BMI; some national guidelines use 23 and 27.5 as action points. This tool shows the international categories.
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