BMI Calculator
Check your body mass index from your height and weight in metric or imperial units, see which WHO category it falls in, and find the healthy weight range for your height — with the working shown.
Calculate your BMI
An example is worked out below — change the figures and it updates.
Your BMI, its category and the working will appear here.
A number you can act on
Your BMI, its category, and the range that matters.
Your BMI to one decimal
The standard weight-divided-by-height-squared figure, calculated the WHO way.
WHO categories
Underweight, normal, overweight and obese — the adult ranges used worldwide.
Healthy weight range
The weights that would put someone of your height inside the normal BMI band.
About this BMI calculator
BMI — body mass index — is your weight in kilograms divided by the square of your height in metres. It was designed as a population screening measure: quick to calculate, roughly correlated with body fat, and easy to compare across large groups. The World Health Organization’s adult categories — under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, 30 and above obese — are the ranges this calculator uses, along with the equivalent healthy weight range for your height.
Use it with its limits in mind. BMI does not measure body fat directly and cannot tell muscle from fat, so muscular people can score as overweight while carrying little fat, and older adults can score as normal while carrying more fat than is healthy. It is also an adult measure: children and teenagers are assessed with age-specific growth charts instead. Treat the result as a starting point for a conversation about health, not a diagnosis — a clinician who can measure waist circumference, body composition and other markers will always give a fuller picture.
Frequently asked questions
The formula, the categories, and where BMI falls short.
How is BMI calculated?
BMI = weight (kg) / height (m) squared. For example, 70 kg at 1.75 m is 70 / 3.0625 = 22.9. In imperial units the same index is 703 x weight (lb) / height (in) squared — this calculator does either, and shows the working.
What is a healthy BMI?
For adults, the WHO normal range is 18.5 to 24.9. The results also show the healthy weight range for your exact height, which many people find more useful than the index itself.
Is BMI accurate for athletes and muscular people?
Often not. Muscle is denser than fat, so a muscular build can push BMI into the overweight band without excess fat. BMI is a population screening tool; individual assessment needs more than one measure.
Can I use this BMI calculator for a child?
No — children and teenagers need BMI-for-age growth charts, because healthy ranges change as they grow. This calculator uses the adult WHO categories only.
Why does my BMI differ from my doctor’s or an app’s?
Usually rounding or units: a height entered in centimetres where metres were expected, or pounds treated as kilograms. This page shows its working, so you can check exactly what was calculated.
Are my height and weight stored?
No. The calculation runs in your browser and nothing you enter is uploaded or saved.