BMI Calculator
Work out your body mass index from your height and weight, see which category it falls in, and find the healthy weight range for someone your height.
Fill in the fields to see your result.
How BMI works
Body mass index is one of the simplest measurements in medicine: your weight divided by your height squared. That's the whole thing. It was devised in the 1830s by a Belgian mathematician studying populations, and it survives today because it needs nothing but a set of scales and a tape measure.
Its simplicity is both why it's everywhere and why it gets criticised. BMI knows how heavy you are. It has no idea what that weight is made of.
The formula
A worked example: someone 1.75 m tall weighing 72 kg has a BMI of 72 / (1.75 x 1.75) = 23.5, which sits comfortably inside the normal band.
What the categories mean
These are the World Health Organization's classifications for adults aged 20 and over. They are the same for men and women.
| BMI | Category |
|---|---|
| Below 16 | Severe thinness |
| 16 – 17 | Moderate thinness |
| 17 – 18.5 | Mild thinness |
| 18.5 – 25 | Normal |
| 25 – 30 | Overweight |
| 30 – 35 | Obese, class I |
| 35 – 40 | Obese, class II |
| Above 40 | Obese, class III |
What BMI gets wrong
It's worth knowing the limits before you take the number to heart.
- It can't tell muscle from fat. Muscle is denser, so a lean, well-trained person can land in the overweight or even obese band while carrying very little fat. Most professional athletes would be classified as overweight by BMI alone.
- It ignores where the weight sits. Fat around the middle carries more health risk than the same amount elsewhere, and BMI can't see the difference. A waist measurement adds information BMI simply doesn't have.
- It shifts with age. Older adults tend to lose muscle and gain fat while their weight stays flat, so an unchanged BMI can hide a real change in body composition.
- The thresholds aren't universal. The WHO has noted that people of Asian descent can face raised risk at a lower BMI, and several countries use lower cut-offs as a result.
- It says nothing about health. Blood pressure, blood sugar, fitness, sleep and diet all matter more than this one ratio, and BMI measures none of them.
None of that makes it useless. It's a fast, free first look that tells you whether a longer conversation is worth having. Just don't mistake it for a diagnosis.
Finding your healthy weight range
Because the formula runs in both directions, you can turn it around: multiply the healthy BMI range by your height squared and you get the weight range that lands you inside it.
The calculator above does this for you and shows the range in whichever unit you picked. For someone 1.75 m tall it works out at roughly 57 to 76 kg — a span of nearly 20 kg, which is a useful reminder that "healthy weight" is a range, not a target.
Frequently asked questions
Is BMI actually accurate?
It's accurate at what it measures, which is weight relative to height — nothing more. BMI was designed in the 1830s to describe populations, not individuals, and it has no way of knowing what your weight is made of. For most people who aren't especially muscular it lands in roughly the right place, and it's useful as a starting point. It is not a measure of health, and a single number was never going to be.
Why does BMI treat muscle and fat the same?
Because it only knows two things about you: how tall you are and how heavy you are. Muscle is denser than fat, so a lean, well-trained person can weigh enough to land in the overweight or obese band while carrying very little body fat. This is the single biggest flaw in BMI and the reason athletes should ignore it. A body fat percentage or a waist measurement will tell you far more.
Does BMI work for children and teenagers?
Not with these categories. Children's body composition changes constantly as they grow, so a child's BMI is compared against percentile charts for their exact age and sex rather than against fixed numbers. The adult bands on this page would give a misleading and potentially upsetting answer for anyone under 20. If you enter an age below 20 here, the calculator shows the number but withholds the category for exactly that reason.
Is the BMI scale different for men and women?
No. The WHO thresholds are identical for adult men and women, which is itself a limitation worth knowing about — women naturally carry a higher percentage of body fat than men at the same BMI. The number means the same thing on paper for both, but what it implies about body composition differs.
Do the thresholds change depending on ethnicity?
For some populations, yes. The WHO has noted that people of Asian descent can face raised health risks at a lower BMI than the standard cut-offs suggest, and several countries use lower thresholds as a result — often treating around 23 as the point where risk begins rather than 25. This calculator shows the standard international bands. If a lower threshold applies where you live, your doctor will use that one.
Are my numbers sent anywhere?
No. Everything is worked out inside your own browser. Nothing you type is uploaded, stored or shared, and there's no sign-up.
Please note: CalcuLane gives estimates for general information only and is not medical advice, a diagnosis or a treatment plan. BMI is a rough screening measure that cannot distinguish muscle from fat and says nothing about your overall health. Formula and categories follow the World Health Organization classification for adults aged 20 and over. Always speak to a doctor or qualified health professional about your own health.