BMI Calculator
Body mass index with category and healthy weight range.
Free BMI calculator for metric and imperial units. Get your body mass index, WHO weight category, and the healthy weight range for your height.
BMI is a screening tool, not a diagnosis. It cannot distinguish muscle from fat, and it is not valid for children, pregnant people, or athletes.
Your BMI
22.9
Normal weight
BMI categories (WHO)
| Category | BMI range | Weight at your height |
|---|---|---|
| Underweight | Below 18.5 | Under 57 kg |
| Normal weightYou | 18.5 – 24.9 | 57 kg – 76 kg |
| Overweight | 25.0 – 29.9 | 77 kg – 92 kg |
| Obese | 30.0 and above | Over 92 kg |
How the BMI Calculator works
Body mass index compares your weight to your height as a quick population-level screening number. It is useful as a starting point, but it cannot tell muscle from fat, which is why an athlete and a sedentary person can share a BMI and very different health profiles.
Also known as: body mass index calculator · am I a healthy weight · BMI chart calculator
Where BMI came from
The formula was devised in the 1830s by Adolphe Quetelet, a Belgian mathematician and statistician, as a way of describing the distribution of body size in populations. It was not intended as a measure of individual health.
It was renamed the body mass index in 1972 by Ancel Keys, who evaluated several indices and found it the best available proxy for body fatness in population studies, while explicitly noting it was inappropriate for individual diagnosis.
Weight in kilograms divided by height in metres squared. In imperial units, weight in pounds times 703 divided by height in inches squared. That is the whole calculation, and its simplicity is both why it spread and why it is limited.
The categories
Under 18.5 is underweight. From 18.5 to 24.9 is the healthy range. From 25 to 29.9 is overweight. Thirty and above is obesity, subdivided into class 1 up to 34.9, class 2 up to 39.9, and class 3 above 40.
The WHO has published lower action points for Asian populations, commonly 23 for increased risk and 27.5 for high risk, reflecting evidence that metabolic risk begins at lower BMI values in South Asian and several East Asian populations.
The boundaries are conventions applied to a continuous measure. Risk does not change at 25; it rises gradually, and someone at 24.9 is not meaningfully different from someone at 25.1.
What it cannot see
Muscle and fat are both weight, and BMI cannot distinguish them. Muscular individuals are routinely classified as overweight or obese with low body fat, which is the criticism most often raised and it is correct.
It also cannot see fat distribution, which matters considerably for metabolic risk. Abdominal fat carries more risk than fat on the hips and thighs, and BMI is blind to the difference.
The reverse error is less discussed and more common: older adults who have lost muscle can sit comfortably in the healthy range while carrying a high proportion of body fat, sometimes called normal weight obesity. BMI reassures them incorrectly.
Why it is still used
It is free, needs no equipment beyond scales and a tape measure, is reproducible, and correlates reasonably with body fatness across large populations.
The epidemiological evidence linking BMI categories to outcomes is enormous, accumulated over decades, and no alternative measure has anything comparable. That evidence base is what makes the categories interpretable at all.
For screening a population it works. For describing an individual it is a starting point that should be read alongside a waist measurement, which adds the distribution information BMI lacks and takes thirty seconds.
What to use alongside it
Waist to height ratio is the single most useful addition, with a memorable threshold: keep your waist under half your height. NICE now recommends it alongside BMI for adults with a BMI under 35.
Waist circumference alone works nearly as well and is simpler still. Both capture central adiposity, which is what BMI misses.
Beyond measurement, the things that actually determine cardiometabolic risk are blood pressure, lipids, blood glucose, fitness and smoking status. A person with a BMI of 27 who is fit, normotensive and metabolically healthy is in a very different position from someone at the same BMI who is none of those, and no body index distinguishes them.
The WHO categories on one scale
Where to go next
The BMI question rarely arrives on its own. These are the ones that usually come with it:
- Body Fat Calculator — Body fat percentage from tape measurements.
- Ideal Weight Calculator — Target weight from four clinical formulas plus BMI range.
- Calorie & BMR Calculator — Daily calorie needs for losing, holding, or gaining weight.
- VDOT Running Calculator — One race result, every training pace.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How is BMI calculated?
BMI = weight in kilograms ÷ (height in metres)². In imperial units, BMI = 703 × weight in pounds ÷ (height in inches)². A 70 kg person who is 1.75 m tall has a BMI of 70 ÷ 3.06 = 22.9.
What is a healthy BMI range?
The WHO classifies BMI under 18.5 as underweight, 18.5-24.9 as normal weight, 25-29.9 as overweight, and 30 or above as obese. For people of South and East Asian descent, health risk rises earlier, and many guidelines shift the overweight threshold down to 23.
Is BMI accurate for everyone?
No. It overestimates body fat in muscular people and underestimates it in older adults who have lost muscle. It is also not valid for children, pregnant people, or anyone under about 18 without age-and-sex-specific percentile charts.
What should I use instead of BMI?
Waist circumference and waist-to-height ratio track health risk better because they capture abdominal fat specifically. A simple rule of thumb: keep your waist under half your height.
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Related calculators
Body Fat Calculator
Body fat percentage from tape measurements.
OpenIdeal Weight Calculator
Target weight from four clinical formulas plus BMI range.
OpenCalorie & BMR Calculator
Daily calorie needs for losing, holding, or gaining weight.
OpenVDOT Running Calculator
One race result, every training pace.
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