BMI Calculator
Check your body mass index and see which healthy-weight range you fall into.
Your BMI
—
BMI is a general screening tool, not a diagnosis. It does not account for muscle mass, body composition, or age. Consult a healthcare professional for medical advice.
Body Mass Index divides your weight by the square of your height to give a quick, standardised way to categorise body weight as underweight, normal, overweight, or obese. It's the same formula used by the WHO and most healthcare providers for population-level screening.
Switch between metric (cm/kg) and imperial (ft/lb) units, and the tool shows your BMI, its category, and the healthy weight range for your height on the same scale doctors use.
The WHO categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
Some health authorities in South and East Asia use lower thresholds — often 23 for overweight and 27.5 for obesity — because cardiometabolic risk rises at a lower BMI in these populations.
What BMI genuinely cannot tell you
BMI was devised in the 19th century to describe populations, not to assess individuals, and it has been doing a job it was never designed for ever since. It takes two numbers and cannot distinguish between the things that actually matter.
- It can't tell muscle from fat. A well-trained athlete frequently lands in the 'overweight' band with very low body fat.
- It can't tell where fat is stored. Visceral fat around the organs carries far more metabolic risk than the same weight carried on hips and thighs.
- It's less reliable for older adults, who lose muscle mass, and for very tall or very short people, because the height-squared term doesn't scale perfectly.
- It is not valid for children and teenagers, who need age-and-sex-specific percentile charts instead.
- It should not be used during pregnancy.
Measurements that add useful context
Waist circumference is the single most useful companion measurement, because it picks up the abdominal fat that BMI is blind to. Measure at the midpoint between the lowest rib and the top of the hip bone, breathing out normally.
As general guidance, a waist above 94 cm (37 in) for men or 80 cm (31.5 in) for women indicates raised risk, with higher thresholds again at 102 cm and 88 cm. Waist-to-height ratio is an even simpler check: keeping your waist under half your height is a reasonable target for most adults.
Frequently asked questions
- Is BMI accurate for everyone?
- BMI is a screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so very muscular people or athletes can show a high BMI while being perfectly healthy. It's also less reliable for children, older adults, and pregnant people.
- What is considered a healthy BMI?
- For most adults, a BMI between 18.5 and 24.9 is classed as a healthy weight range by the WHO.
- How do I calculate BMI by hand?
- Metric: weight (kg) ÷ height (m)². Imperial: 703 × weight (lb) ÷ height (in)².
- Why do some doctors use a lower BMI threshold for Asian patients?
- Research has found that risk of type 2 diabetes and cardiovascular disease rises at a lower BMI in South and East Asian populations, so several health authorities use 23 rather than 25 as the overweight threshold.
- Should I use BMI or body fat percentage?
- Body fat percentage is more informative but harder to measure accurately — home scales using bioimpedance can be off by several points. BMI plus a waist measurement is a practical combination for most people.
- Is this medical advice?
- No. This is a screening calculator for general information. Any decision about your weight or health should involve a qualified healthcare professional who can look at the full picture.
Read more on this
- BMI explained: what the number means and when to ignore itHow BMI is calculated, where the WHO weight categories come from, a worked example, and the specific situations — muscle mass, ethnicity, age — where the number stops being useful.
- How to calculate TDEE and set a safe calorie deficitThe four components of daily energy expenditure, calculating BMR with the Mifflin-St Jeor formula, and why aggressive calorie cutting stalls progress.