BMI Calculator
Body mass index (BMI) is your weight in kilograms divided by the square of your height in meters. For adults, 18.5 to 24.9 is classed as a healthy weight.
Type a number and the answer appears straight away.
Body mass index23.6Healthy weight
- Underweight under 18.5
- Healthy 18.5-25
- Overweight 25-30
- Obesity 30+
- Healthy range for your height
- 125.3 lb to 168.6 lb
- Healthy BMI range
- 18.5 to 24.9
BMI is a screening measure for adults. It does not distinguish muscle from fat.
The math behind it: BMI
BMI = weight (kg) / height (m)² or BMI = 703 x weight (lb) / height (in)²
Someone who is 5 ft 9 in (175 cm) and weighs 160 lb (72.6 kg) has a BMI of 23.6, inside the healthy range.
BMI categories for adults
The World Health Organization and the US Centers for Disease Control and Prevention use the same cut-off points for adults aged 20 and over, regardless of sex or age.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25.0 to 29.9 | Overweight |
| 30.0 to 34.9 | Obesity, class 1 |
| 35.0 to 39.9 | Obesity, class 2 |
| 40.0 and above | Obesity, class 3 |
What BMI is good for
BMI is quick, free and needs nothing more than a scale and a tape measure. Across large groups of people it tracks closely with body fat and with the risk of conditions such as type 2 diabetes, high blood pressure and heart disease. That makes it a useful first screen.
Where BMI falls short
BMI measures weight, not fat. It cannot tell muscle from fat, and it says nothing about where fat is carried. As a result it can mislead in several situations:
- Muscular people, including many athletes, can land in the overweight band with low body fat.
- Older adults who have lost muscle can have a healthy BMI while carrying excess fat.
- Health risk at a given BMI differs between ethnic groups. Some health bodies use lower thresholds for people of South Asian, Chinese and other Asian backgrounds.
- It is not used in the same way for children and teenagers, who are assessed against age- and sex-specific growth charts.
- It does not apply during pregnancy.
Waist measurement adds useful information, because fat around the abdomen carries more risk than fat elsewhere. For a fuller picture, try the body fat calculator, which estimates fat percentage from a few tape measurements.
How to use your result
Treat BMI as a conversation starter rather than a diagnosis. If your result is outside the healthy range, or you are concerned about your weight either way, a doctor or registered dietitian can look at it alongside your waist size, blood pressure, blood tests and family history.
Common questions
What is a healthy BMI?
For adults, a BMI from 18.5 to 24.9 is classed as a healthy weight.
Is BMI different for men and women?
The formula and categories are the same. Women tend to have more body fat than men at the same BMI, which is one reason BMI is treated as a screening tool only.
How much should I weigh for my height?
The calculator shows the weight range that corresponds to a BMI of 18.5 to 24.9 at your height. For formula-based estimates see the ideal weight calculator.
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