You can use the Body Mass Index to find out if you’re a healthy weight for your height.

These are the weight ranges, set by the World Health Organisation:

  • If your BMI is less than 18.4 you are underweight for your height.
  • If your BMI is between 18.5 and 24.9 you’re an ideal weight for your height.
  • If your BMI is between 25 and 29.9 you’re over the ideal weight for your height.
  • If your BMI is between 30 and 39.9 you’re obese.
  • If your BMI is over 40 you’re very obese.

If your BMI is over 25 you do need to think about losing weight, otherwise you’re at risk of health problems. If its over 30 you need to make some big changes to your lifestyle to get your weight down.

  • When you work out your BMI, remember to take into account your body frame and your build – your BMI may not be accurate if you are a weight-trainer or an athlete, or if you are pregnant or breastfeeding.
  • Your BMI may not be accurate if you are over the age of 60. This is because your bones may begin to weigh less as you get older.

Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI provides a reliable indicator of body fatness for most people and is used to screen for weight categories that may lead to health problems. Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI is a reliable indicator of body fatness for people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat. BMI can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems. Calculating BMI is one of the best methods for population assessment of overweight and obesity. Because calculation requires only height and weight, it is inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population. BMI is calculated the same way for both adults and children. The calculation is based on the following formulas:

Measurement Units Formula and Calculation

Kilograms and meters (or centimeters)

Formula: weight (kg) / [height (m)]2

With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.

Example: Weight = 68 kg, Height = 165 cm (1.65 m) Calculation: 68 ч (1.65)2 = 24.98

Pounds and inches

Formula: weight (lb) / [height (in)]2 x 703

Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.

Example: Weight = 150 lbs, Height = 5’5” (65″) Calculation: [150 ч (65)2] x 703 = 24.96

The standard weight status categories:

BMI Weight Status
Below 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and Above Obese

The correlation between the BMI number and body fatness is fairly strong and varies by sex, race, and age. For example:

  • At the same BMI, women tend to have more body fat than men.
  • At the same BMI, older people, on average, tend to have more body fat than younger adults.
  • Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness.

The BMI ranges are based on the relationship between body weight and disease and death. Overweight and obese individuals are at increased risk for many diseases and health conditions, including the following: 

  • Hypertension
  • Dyslipidemia
  • Type 2 diabetes
  • Coronary heart disease
  • Stroke
  • Gallbladder disease
  • Osteoarthritis
  • Sleep apnea and respiratory problems
  • Some cancers (endometrial, breast, and colon)