BMI Calculator
Enter your height and weight and this gives your BMI, which band it falls in, and the weight range that would put you in the healthy band at your height.
Healthy weight
22.9BMI
- BMI
- 22.9
- Category
- Healthy weight
- Healthy from
- 56.7 kg
- Healthy to
- 76.3 kg
- BMI is a screening measure across populations, not a diagnosis of an individual. It takes no account of muscle, frame or fat distribution, so a muscular person can read as overweight while carrying very little fat.
- These bands apply to adults. Children are assessed against age-and-sex percentile charts, which is a clinical judgement rather than arithmetic.
About the BMI calculator
Body mass index is weight divided by height squared. It was designed in the nineteenth century to describe populations, not individuals, and that is still what it does best — it is a fast screening number, not a diagnosis.
The limitation is well known and worth stating plainly: BMI cannot tell muscle from fat. A trained athlete often reads as overweight while carrying very little fat, and someone sedentary can sit in the healthy band with a lot of it. Where the weight sits on the body matters too, and BMI has nothing to say about that.
It is still useful, because it is quick, it needs no equipment, and at a population level it tracks health outcomes well enough to be worth a look. Treat a reading near a band edge as roughly nothing, and a reading far from the middle as worth a conversation with a doctor.
What it works out
- Your BMI and which band it falls in
- The healthy weight range for your height
- Metric or imperial input
- Adults only — not children
The formula
BMI = weight in kg ÷ (height in metres)²
Weight in kilograms divided by height in metres squared. The imperial version multiplies by 703 to make pounds and inches work, but it is the same calculation underneath and gives the same number.
The squaring is where the criticism comes from. Body mass scales closer to height cubed than squared, so tall people read slightly high and short people slightly low on the same build. It is a known distortion rather than a mistake, and it is small next to the muscle-versus-fat problem.
The bands are conventional rather than derived: under 18.5 underweight, 18.5 to 25 healthy, 25 to 30 overweight, 30 and above obese. They are drawn from population studies of health outcomes and the boundaries are round numbers, so a reading of 24.9 and one of 25.1 mean essentially the same thing.
- Weight
- In kilograms. Pounds are converted for you.
- Height
- In metres. The formula squares it, so measure carefully — a centimetre out moves the answer.
- BMI
- The resulting index, with no units of its own.
A worked example
Seventy kilograms at a hundred and seventy-five centimetres.
That works out to 22.9 BMI.
- BMI
- 22.9
- Category
- Healthy weight
- Healthy from
- 56.7 kg
- Healthy to
- 76.3 kg
Questions
What is a healthy BMI?
Between 18.5 and 24.9 for adults. Below that is classed as underweight and 25 or above as overweight, with 30 and above classed as obese. The boundaries are round numbers drawn from population data, so a reading either side of one means much the same thing.
Is BMI accurate for athletes?
No. Muscle is denser than fat, so a well-trained person often reads as overweight or even obese while carrying very little fat. If you lift seriously, a tape measurement or a body fat estimate tells you far more.
Does BMI work for children?
Not in this form. Children are assessed against age-and-sex percentile charts because healthy body composition changes throughout growth. That is a clinical assessment, and this calculator is for adults only.
How do I work out BMI in pounds and inches?
Weight in pounds divided by height in inches squared, multiplied by 703. Switching this calculator to imperial does it for you and gives the same number as the metric version.
What weight should I be for my height?
The calculator shows the range that puts you between 18.5 and 24.9. For 175cm that is roughly 57kg to 76kg — a wide span, which reflects how little BMI knows about build.
Should I worry about a high BMI?
It is a reason to look further, not a diagnosis. Waist measurement, blood pressure, activity and family history all tell you more. Take a reading well outside the healthy band to a doctor rather than acting on it alone.