How Do You Calculate Ideal Body Weight? IBW

Medically Reviewed on 11/3/2021
how do you calculate ideal body weight
Knowing your ideal body weight (IBW) can help you determine a weight management goal. Learn how to calculate ideal body weight

Whether you are trying to lose, gain, or maintain weight, knowing your ideal body weight (IBW) can help you figure out a goal. Your ideal body weight is determined by genetics, age, gender, and muscle mass

How much body fat you have can help you understand your risk of diseases such as diabetes, heart diseases, and cancer, which can be associated with obesity.

Formulas for calculating ideal body weight

Various methods and formulas can be used to calculate IBW. You are considered obese if you 30% more than your IBW. A common formula is as follows:

  • Men: IBW (kgs) = 22 × (height in meters)2
  • Women: IBW (kgs) = 22 × (height in meters − 10 cm)2

The following formulas were developed to calculate drug dosages:

  • GJ Hamwi's formula (1964)
    • Men: 48.0 kg + 2.7 kg per inch over 5 feet
    • Women: 45.5 kg + 2.2 kg per inch over 5 feet
  • BJ Devine's formula (1974)
    • Men: 50.0 kg + 2.3 kg per inch over 5 feet
    • Women: 45.5 kg + 2.3 kg per inch over 5 feet
  • JD Robinson's formula (1983)
    • Men: 52 kg + 1.9 kg per inch over 5 feet
    • Women: 49 kg + 1.7 kg per inch over 5 feet
  • DR Miller's formula (1983)
    • Men: 56.2 kg + 1.41 kg per inch over 5 feet
    • Women: 53.1 kg + 1.36 kg per inch over 5 feet

What are other methods for calculating ideal body weight?

Body mass index (BMI)

BMI is used to determine whether your body weight is healthy and calculates your weight based on your height. The formula for calculating BMI is as follows:

[Weight (kg) / height (cm) / height (cm)] × 10,000 = BMI

Both low and high BMI values indicate poor health:

  • Underweight: BMI of less than 18.5 kg/m2
  • Normal or ideal: BMI of between 18.5 and 24.9 kg/m2
  • Overweight: BMI of between 25 and 29.9 kg/m2
  • Obese: BMI over 30 kg/m2

However, there is a downside to BMI because it does not consider healthy muscle mass, fat distribution, and pelvic measurements.

For example, an athlete may have high muscle mass, but it is calculated as weight. As a result, their BMI measurement may indicate that the athlete is obese when they are actually healthy. Moreover, women and older men tend to store more fat than younger men.

Weight-to-hip ratio (WHR)

Reports have suggested that WHR may be better than BMI at assessing the risk of cardiovascular diseases and premature death. WHR measures the narrowest portion of the waist, directly above the navel, divided by the circumference of the hip at its broadest point:

WC (waist circumference) / HC (hip circumference at the broadest point) = waist-to-hip ratio

According to the World Health Organization, a good WHR ratio is as follows:

  • Men: 0.9 or less
  • Women: 0.85 or less

Irrespective of sex, if a person has WHR higher than 1.0, that person is overweight and may have a higher risk of developing cardiovascular diseases.

Calculating WHR may be difficult, however, because taking accurate hip measurements poses a challenge. For example, a person may have a greater WHR because of accumulated weight around the abdomen, but that weight could be either fat or muscle around the hips as a result of exercise.

Body fat percentage

When measuring body fat percentage, a health professional should measure thighs, abdomen, and chest in men and upper arm circumference in women. The range of accuracy should be 3.5%. To calculate body fat percentage:

WBD (weight of body fat) / TW (total weight) = body fat percentage

According to the American Council on Exercise, healthy essential body fat composition is as follows:

  • Men: 2%-4%
  • Women: 10%-30%

Other ways to determine body fat percentage include

  • Underwater weighing or hydrostatic body fat measurement
  • Measurement of air displacement (air densitometry)
  • Dual energy X-ray absorptiometry
  • Bioelectrical impedance analysis

None of these may provide an entirely accurate reading, but the estimations are close enough to provide a realistic evaluation.


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Medically Reviewed on 11/3/2021
Image Source: Hailshadow / Getty Images Ideal Weight Calculator.

Peterson CM, Thomas DM, Blackburn GL, Heymsfield SB. Universal equation for estimating ideal body weight and body weight at any BMI [published correction appears in Am J Clin Nutr. 2017 Mar;105(3):772]. Am J Clin Nutr. 2016;103(5):1197-1203.