BMI Calculator: Check Your Body Mass Index
Your BMI (body mass index) tells you whether your weight is in a healthy range. It is more useful than your weight alone, because it takes your height into account.
In Europe, a BMI over 25 is considered overweight and a BMI over 30 as obese. Carrying excess weight can raise your total cholesterol and blood pressure, and increase your risk of coronary heart disease.
Calculate your BMI
Enter your weight and height to see your BMI.
This calculation is for adults only.
BMI Classification
| BMI | Classification |
|---|---|
| < 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25 - 26.9 | Overweight grade I |
| 27 - 29.9 | Overweight grade II (pre-obesity) |
| 30 - 34.9 | Obesity type I |
| 35 - 39.9 | Obesity type II |
| 40 - 49.9 | Obesity type III (morbid) |
| ≥ 50 | Obesity type IV (extreme) |
SEEDO classification (Sociedad Española para el Estudio de la Obesidad, the Spanish society for the study of obesity). It has eight categories, whereas the WHO classification has only four.
How Is BMI Calculated?
BMI is calculated with a single formula, which is the same for men and women.
BMI = weight (kg) ÷ height (m)²
Someone who weighs 76 kg and is 1.75 m tall has a BMI of 76 ÷ (1.75 × 1.75) = 24.8, which is within the normal weight range.
For an accurate reading, use a good-quality scale first thing in the morning, after emptying your bladder and bowels, on an empty stomach and in your underwear. BMI only applies to adults.
At What BMI Can Weight Loss Surgery Be Considered?
A single number is never enough to decide on bariatric surgery. In Europe, the usual criteria are a BMI of 40 or more, or a BMI of 35 or more together with a weight-related condition: type 2 diabetes, high blood pressure, sleep apnea, disabling osteoarthritis or fatty liver disease.
Joint guidelines published by ASMBS and IFSO in 2022 lowered these thresholds. They recommend surgery from a BMI of 35 even without a related condition, and consider it between 30 and 35 when type 2 diabetes remains poorly controlled despite medical treatment.
BMI alone decides nothing: it is the starting point for a conversation. Whether surgery is right for you is decided at your consultation, after an assessment that looks at your weight history, previous attempts to lose weight, your metabolic health and what you are hoping for.
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Questions
Common Questions About BMI
How does the BMI calculator work?
Enter your weight in kilograms and your height in centimeters or meters. The calculator divides your weight by your height squared, then shows your result, its classification and the weight range that would give you a normal BMI for your height. The calculation runs in your browser: we do not store any data.
How should I read my BMI?
A BMI between 18.5 and 24.9 is considered a normal weight, and below 18.5 is underweight. Between 25 and 29.9 is overweight, and 30 or above is obesity, with four grades of increasing severity up to extreme obesity at over 50. A high BMI points to a higher statistical risk, not an individual diagnosis.
Is BMI reliable?
Only partly. BMI is a screening tool, not a measure of body composition. It cannot tell fat from muscle: a very muscular athlete can have an overweight BMI without carrying excess fat. It is of limited use in older people, who gradually lose muscle mass, and it does not apply to children, teenagers or pregnant women. Even so, it remains the standard tool for the general population, because it is simple, reproducible and linked to cardiovascular risk.
What is the ideal weight for my height?
Ideal weight is a range rather than a single number: the range that gives a BMI between 18.5 and 24.9. At 1.70 m, that is roughly 53 to 72 kg, and at 1.80 m, roughly 60 to 81 kg. The calculator shows this range for your height automatically.
Should I measure my waist as well?
Yes, it is a useful extra check. BMI tells you nothing about where your fat is stored, and it is fat around the abdomen that has the greatest impact on metabolic risk. A waist measurement over 94 cm in men or 80 cm in women indicates increased risk, even with a normal BMI. Above 102 cm in men and 88 cm in women, the risk is substantially higher.
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