How Much Should I Weigh?
Most everyone has at some point tried to lose weight, or at least known somebody who has. This is largely due to the perception of an "ideal" body weight, which is often based on what we see promoted through various media such as social media, TV, movies, magazines, etc.
Although ideal body weight (IBW) today is sometimes based on perceived visual appeal, IBW was actually introduced to estimate dosages for medical use, and the formulas that calculate it are not at all related to how a person looks at a given weight. It has since been determined that the metabolism of certain drugs is more based on IBW than it is total body weight.
Factors Affecting Ideal Weight
Gender
Generally, females weigh less than males even though they naturally have a higher percentage of body fat. This is because the male body generally has higher muscle mass, and muscle is heavier than fat. Not only that, but women generally have lower bone density.
Height
The taller the person, the more muscle mass and body fat they have, which results in more weight. A male at a similar height to a female should weigh about 10-20% heavier.
Formulas for Finding Ideal Weight
IBW formulas were developed mainly to facilitate drug dosage calculations. All of the formulas have the same format of a base weight given a height of 5 feet, with a set weight increment added per inch over the height of 5 feet.
G. J. Hamwi Formula (1964)
- Male: 48.0 kg + 2.7 kg per inch over 5 feet
- Female: 45.5 kg + 2.2 kg per inch over 5 feet
B. J. Devine Formula (1974)
- Male: 50.0 kg + 2.3 kg per inch over 5 feet
- Female: 45.5 kg + 2.3 kg per inch over 5 feet
J. D. Robinson Formula (1983)
- Male: 52 kg + 1.9 kg per inch over 5 feet
- Female: 49 kg + 1.7 kg per inch over 5 feet
Peterson Formula (2016)
A modern formula that accounts for BMI targets more dynamically.
- IBW = 2.2 · BMI_target + 3.5 · BMI_target · (Height_m - 1.5)
- (Usually calculated with a target BMI of 22)
Frame Size and Weight
One of the biggest criticisms of standard IBW formulas is that they don't account for "bone structure" or frame size. A person with a large frame can healthily weigh significantly more than a person with a small frame at the same height.
| Frame Size | Wrist Circumference (Inches) |
|---|---|
| Small | Less than 6.25" (Women) / 6.5" (Men) |
| Medium | 6.25" - 6.5" (Women) / 6.5" - 7.5" (Men) |
| Large | Over 6.5" (Women) / 7.5" (Men) |
Healthy BMI Range
The World Health Organization (WHO) recommended healthy BMI range is 18.5 - 25 for both males and females. Based on the BMI range, it is possible to find out a healthy weight for any given height.
BMI is a commonly used metric for determining IBW. It is widely used in the medical field as a quick indicator of possible health complications. However, it does not account for body composition (muscle vs fat).
Limitations of IBW Calculators
There are limitations to all the formulas and methods. Because the formulas are designed to be as applicable to as wide a range of people as possible, they cannot be highly accurate for every single individual. The formulas factor only height and gender, and there are no considerations for physical handicaps, people on the extreme ends of the spectrum, activity levels, or muscle mass to body fat ratio.
Note for Athletes: If you have high muscle mass, these calculators will almost certainly label you as "overweight" even if you have very low body fat. In these cases, Body Fat Percentage is a much better indicator of health than Ideal Weight or BMI.