BMI Calculator — Body Mass Index for Adults
Calculate your body mass index in metric or imperial units, see your WHO weight category and the healthy weight range for your height, with the limits of BMI explained.
For adults aged 18 and over. BMI is a screening measure, not a diagnosis, and it isn't used for children, teenagers or during pregnancy.
Your BMI
22.7
Healthy weight
A healthy weight for your height is between 125 lb and 169 lb.
| Underweight | < 18.5 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity class I | 30 – 34.9 |
| Obesity class II | 35 – 39.9 |
| Obesity class III | ≥ 40 |
What BMI tells you
Body mass index compares your weight with your height to give a single number. At a population level it tracks health risks well: the risks of type 2 diabetes, high blood pressure and heart disease rise steadily as BMI climbs above the healthy range, and some risks rise below it too. That is why doctors use it as a quick first screening step.
The WHO categories
- Below 18.5 — underweight.
- 18.5 to 24.9 — healthy weight.
- 25 to 29.9 — overweight.
- 30 to 34.9 — obesity class I.
- 35 to 39.9 — obesity class II.
- 40 and above — obesity class III.
What BMI can't tell you
BMI knows your weight but not what it's made of. A rugby player and a sedentary person of the same height and weight get the same score, even though one carries far more muscle. It also says nothing about where fat is stored, and fat around the waist is more strongly linked to health problems than fat elsewhere. Treat BMI as a starting point for a conversation with a health professional, not a verdict.
A useful second check
Measure your waist at the midpoint between your lowest rib and the top of your hip bone. Several health authorities now suggest keeping your waist to less than half your height — for someone 175 cm tall, under 87.5 cm. Used together, BMI and waist size give a much better picture than either on its own.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres. For someone who weighs 70 kg and is 1.75 m tall, that's 70 ÷ (1.75 × 1.75) = 22.9. In imperial units the same result comes from 703 × pounds ÷ inches².
What is a healthy BMI?
For adults, the World Health Organization classes 18.5 to 24.9 as a healthy weight, 25 to 29.9 as overweight and 30 or more as obesity. Some health services use lower thresholds for people of South Asian, Chinese and other Asian backgrounds — for example 23 for overweight — because health risks start rising at a lower BMI.
Is BMI accurate for athletes and older people?
Not always. BMI can't tell muscle from fat, so muscular people often score as overweight while being perfectly healthy. Older adults can have a normal BMI while carrying too little muscle. Waist measurement is a useful second check: a waist of more than half your height is linked to higher health risk.
Can I use this for children or during pregnancy?
No. Children and teenagers are assessed with BMI-for-age percentile charts, because healthy body composition changes as they grow. During pregnancy, weight gain is expected and is tracked differently. Your doctor or midwife can advise in both cases.
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Last updated September 25, 2026