Body mass index, or BMI, is one way a person can check if their weight is healthy or not. BMI takes both height and weight into consideration.
Carrying too much or too little weight can increase a person’s risk of health problems, either now or in the future.
BMI is not the only factor that affects this risk. Other tools for assessing whether a person has a healthy weight include waist-to-hip ratio, waist-to-height ratio, and body-fat percentage.
However, BMI is a useful starting point. This page provides some tools for people to work out their BMI.
These calculators and charts can give an indication of whether a person’s weight may affect their risk of health problems.
We are publishing the calculators here courtesy of The Calculator Site. There are two calculation options available: Metric and imperial.
To use the charts below, find your weight in pounds along the top and your height in feet and inches down the side. Then look across to find your BMI.
There are two charts. If a person’s weight is 200 pounds (lb) or under, they should use the first chart. If their weight is over 200 lb, they should look at the second one.
The shaded areas correspond to BMI values that indicate either a healthy weight, excess weight, or obesity.
In addition researchers and clinicians divide obesity into three categories.
- Class I: BMI is 30 to 34.9
- Class II: BMI is 35 to 39.9
- Class III: BMI is 40 and above
The charts are an adaptation of the Adult body mass index (BMI) chart. created by the University of Vermont, in the United States.
Body mass index chart: Weight from 95–245 pounds
Adult BMI chart showing ranges “under healthy weight: BMI <18.5,” “healthy weight: BMI 18.5–24” and “overweight: BMI 25–29.9.”
Body mass index chart: Weight from 250–400 pounds
Adult BMI chart showing ranges “obese I: BMI 30–34.9,” “obese II: BMI 35–39.9” and “obese III: BMI ≥ 40.”
These figures are only a guide. The BMI tools will not determine whether a person has an ideal body weight, but it can help to show if an individual’s weight is increasing their risk for disease.
A person who is very fit, for example, an Olympic athlete, may have a high BMI.
This does not necessarily mean that they are overweight. The excess weight, in this case, may be due to increased muscle mass.
The following table shows the standard weight status categories associated with BMI ranges for adults:
|30.0 and above||Obese|
A BMI of less than 18.5 indicates that you are underweight, so you may need to put on some weight. You are recommended to ask your doctor or a dietitian for advice.
A BMI of 18.5–24.9 indicates that you are at a healthy weight for your height. By maintaining a healthy weight, you lower your risk of developing serious health problems.
A BMI of 25–29.9 indicates that you are slightly overweight. You may be advised to lose some weight for health reasons. You are recommended to talk to your doctor or a dietitian for advice.
A BMI of over 30 indicates that you are heavily overweight. Your health may be at risk if you do not lose weight. You are recommended to talk to your doctor or a dietitian for advice.
A healthy weight can help prevent a range of diseases and health conditions.
People with a BMI of 30 or more have a higher risk than others of diseases such as heart disease, type 2 diabetes, sleep apnea, high blood pressure, colorectal cancer, for example. Some of these can be life-threatening.
Having a BMI of under 18.5 can increase the risk of malnutrition, osteoporosis, anemia, and a range of problems that can result from various nutrient deficiencies. It can also be a sign of a hormonal, digestive, or other problem.
Evidence suggests that the associations between BMI, percentage of body fat, and body fat distribution may differ across populations, due to variations in race and ethnicity.
A Brazilian study, published in 2017, looked at the correlation between BMI and body-fat percentage in 856 adult men and women.
They concluded that to predict obesity-type body-fat percentage:
- The standard BMI threshold of 29.9 kg/m2 was appropriate for men.
- A more suitable cutoff point for women appeared to be 24.9 kg/m2.
In 2017, Korean researchers pointed out that people in the Asia-Pacific region often have a higher risk of type 2 diabetes and cardiovascular disease at a BMI below the existing WHO cutoff point.
In Korea, they added, there is evidence that almost twice as many people have features of metabolic obesity but a normal weight compared with the U.S.
In 2010, results of a study published in The International Journal of Obesity found that Asian Americans within the healthy weight range were more likely to have symptoms of metabolic syndrome than their non-Hispanic white counterparts.
The following table, published in 2006 by the World Health Organization (WHO), shows some comparisons and cutoff points that may apply.
Doctors may use these variations when treating or advising specific people.
|Classifications||BMI (kg/m2) |
principal cutoff points
additional cutoff points
|Obese class I||30.00–34.99||30.00–32.49|
|Obese class II||35.00–39.99||35.00–37.49|
|Obese class III||≥40.00||≥40.00|
BMI is a useful tool that gives a general idea about whether a person’s weight is healthy or not. However, it is a simple tool that does not tell the whole story about people’s individual weight and health risks.
Anyone who is concerned about their weight should speak to a doctor, who may also consider the individual’s body-fat distribution and the ratio of their waist size to their height. A health professional will also be able to offer advice to suit every individual.