BMI Calculator
Find your Body Mass Index in metric or US units, with the category ranges shown.
Body Mass Index is a quick screening number that relates your weight to your height. It doesn't measure body fat directly, but it's the figure most health guidelines use as a first check because it needs only two measurements anyone can take. Enter your height and weight below — in kilograms and centimetres, or in pounds and inches — and the result updates as you type. Your numbers stay in your browser; nothing is sent anywhere.
The formula
BMI is weight divided by height squared. In metric units that is kilograms divided by metres squared:
BMI = weight (kg) ÷ height (m)²
With US units the same ratio is multiplied by 703 so it works with pounds and inches:
BMI = 703 × weight (lb) ÷ height (in)²
For example, someone who is 175 cm and 70 kg has a BMI of 70 ÷ (1.75 × 1.75) ≈ 22.9, which falls in the normal range.
What the categories mean
The World Health Organization groups adult BMI into four bands: below 18.5 is underweight, 18.5 to 24.9 is the normal range, 25.0 to 29.9 is overweight, and 30.0 or above is in the obese range. These thresholds are the same for men and women. They describe populations well, which is why doctors use them as a starting point, but a single person's healthy weight can sit a little outside the band that BMI alone would suggest.
Where BMI falls short
Because BMI only knows your height and weight, it can't tell muscle from fat. A muscular athlete may score as "overweight" while carrying very little fat, and an older adult who has lost muscle may score as "normal" despite a high fat percentage. It also isn't designed for children, pregnant people, or for comparing across every ethnic group without adjustment. Treat your result as one data point — useful for spotting a trend over time — rather than a verdict, and talk to a clinician for a fuller picture.
Frequently Asked Questions
Is the BMI formula the same for men and women?
Yes. BMI uses only height and weight, so the calculation and the standard category ranges are identical regardless of sex.
Why might a fit, muscular person get an "overweight" result?
BMI cannot distinguish muscle from fat. Muscle is denser than fat, so a very muscular body can push the number into the overweight band even at a low body-fat level. This is a known limitation of the measure.
Does this calculator store my height and weight?
No. The calculation runs entirely in your browser and nothing is uploaded or saved. Reloading or closing the page clears the values.
Should I use BMI for a child?
Adult BMI categories do not apply to children and teens, whose healthy ranges change with age and are read from percentile charts. Ask a paediatrician for the right assessment.