BMI calculator (WHO categories)
Enter your height and weight in imperial or metric units. The calculator shows your BMI, the World Health Organization (WHO) category and the weight range that gives a BMI in the normal range for your height.
Example: Units: imperial (ft, in, lb) · Height (feet) 5 ft · Height (inches) 9 in · Weight (pounds) 154 lb · Age 35 years → Your BMI: 22.7. Source: BMI Prime, Gadzik J (2006): “How much should I weigh?” – Quetelet’s equation, upper weight limits, and BMI prime. Conn Med 70(2):81–88. Updated: .
How it is calculated
How BMI is calculated
BMI = weight in kg ÷ (height in m)². In imperial units the calculator converts first: 1 inch = 2.54 cm and 1 lb = 0.45359237 kg. Example: 5 ft 9 in is 69 in = 175.26 cm, and 154 lb is 69.85 kg, so BMI = 69.85 ÷ (1.7526 × 1.7526) = 22.7. The result is rounded to one decimal place and that rounded value is categorized, so the number and the category always match.
How to calculate your BMI
- Choose metric or US units (feet, inches, pounds).
- Enter your height and weight; age and pregnancy are optional.
- Read your BMI, the WHO category and the healthy weight range for your height.
Example: 160 lb at 5 ft 9 in gives 703 × 160 / 69² = 112,480 / 4,761 ≈ 23.6 – a healthy weight. In metric: 70 kg at 1.75 m is 70 / 1.75² ≈ 22.9.
WHO categories for adults
| BMI | Category |
|---|---|
| below 16.0 | Underweight: severe thinness |
| 16.0 to 16.9 | Underweight: moderate thinness |
| 17.0 to 18.4 | Underweight: mild thinness |
| 18.5 to 24.9 | Normal range |
| 25.0 to 29.9 | Pre-obesity (overweight) |
| 30.0 to 34.9 | Obesity class I |
| 35.0 to 39.9 | Obesity class II |
| 40.0 and above | Obesity class III |
The cut-offs come from the WHO report on obesity (Technical Report Series 894); the grades of thinness from the WHO report on anthropometry (TRS 854). They are the same for women and men.
Healthy weight for your height
Rearranging the formula gives the weight range for a BMI of 18.5 to 24.9: 18.5 × height² to 24.9 × height². At 5 ft 9 in that is about 125.3 to 168.6 lb (56.8 to 76.5 kg).
Limits of BMI
- Muscle mass: BMI only relates weight to height. People with a lot of muscle can have a high BMI without much body fat.
- Fat distribution: belly fat matters more for health than fat on hips and legs. WHO names waist circumference as a useful additional measure.
- Age: body composition shifts over the years; the same BMI often means more fat and less muscle in older adults.
- Children and teenagers: BMI is compared with percentiles for age and sex (WHO reference for ages 5 to 19), not with fixed cut-offs.
- Pregnancy: weight gain is normal, so BMI is not a suitable measure during this time.
BMI is a screening figure, not a diagnosis. It does not replace medical advice.
BMI Prime and weight limits
BMI Prime is your BMI divided by 25, the WHO upper limit of normal weight. Below 1.0 you are under that limit, from 1.0 overweight begins, from 1.2 obesity (BMI 30). Example: BMI 22.9 ÷ 25 = 0.92, so a little over 8% below the upper limit. The value has no unit and makes the distance to the limit easy to compare (Gadzik 2006).
The calculator’s table also shows the weight at which your height reaches the BMI cut-offs 18.5, 25, 30, 35 and 40. At 5 ft 9 in, for example, the normal range ends at about 169 lb (76.6 kg at 1.75 m).
More health calculators: find your healthy weight range with the ideal weight calculator, estimate body fat with the body fat calculator, and work out daily calories with the BMR calculator.
Frequently asked questions
What is a normal BMI?
According to WHO, a BMI of 18.5 to 24.9 is the normal range for adults. Below 18.5 is underweight, 25 and above is pre-obesity (overweight) and 30 and above is obesity.
Is BMI different for men and women?
No. The WHO adult cut-offs are the same for both sexes.
Can I use this BMI calculator for children?
Not with the adult categories. For children and teenagers BMI is compared with percentile charts for age and sex, so under 18 the calculator shows only the number.
Why is my BMI high even though I train a lot?
Muscle is heavy. BMI does not separate muscle from fat, so athletic people are often rated higher than their body fat would suggest.
How much should I weigh for my height?
The normal range is 18.5 × height² to 24.9 × height² (height in meters). At 6 ft 0 in that is roughly 136 to 184 lb.
How do you calculate BMI?
Divide weight in kilograms by height in meters squared: 70 kg / (1.75 × 1.75) ≈ 22.9. In US units, multiply pounds by 703 and divide by height in inches squared.
What BMI is considered overweight?
For adults, the WHO classes a BMI of 25 or more as overweight and 30 or more as obesity. Below 18.5 counts as underweight.
What is BMI Prime?
BMI Prime is BMI divided by 25. A value of 1.0 equals the WHO upper limit of normal weight (BMI 25); below 0.74 is underweight, from 1.2 obesity (BMI 30).
At what weight am I overweight for my height?
From a BMI of 25, which at 1.75 m (5 ft 9 in) is about 76.6 kg (169 lb). The table lists the 18.5, 25, 30, 35 and 40 cut-offs for your height.
Sources and legal basis
- BMI Prime: Gadzik J (2006): “How much should I weigh?” – Quetelet’s equation, upper weight limits, and BMI prime. Conn Med 70(2):81–88
- WHO TRS 894: WHO Technical Report Series 894 – Obesity: preventing and managing the global epidemic (2000), Table 2.1
- WHO TRS 854: WHO Technical Report Series 854 – Physical status: the use and interpretation of anthropometry (1995), grades of thinness
- WHO – Obesity and overweight, fact sheet (definitions for adults and children)
- WHO Growth reference 5–19 years – BMI-for-age
As of: · Editorial policy
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