What Should I Weigh?

Determining your “ideal” weight isn’t as simple as following a one-size-fits-all number. Although media often promote an ideal weight based on looks, the concept of Ideal Body Weight (IBW) originally served a very different purpose—helping to calculate accurate drug dosages. In many medical and sports settings, IBW is still used today because certain medications and athletic classifications depend more on a person’s IBW than their total body weight.

However, IBW is far from a perfect measure. It doesn’t consider how much muscle versus fat you have. For instance, a fit athlete with a high muscle mass might appear “overweight” on paper, even though they’re perfectly healthy. Ultimately, no single formula or metric—whether IBW, BMI, or another measure—can definitively tell you what you should weigh. The focus should instead be on living a healthy lifestyle that includes regular exercise, a balanced diet, sufficient sleep, and stress management.

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Factors That Influence Ideal Weight

Age:
Once you finish growing (around 14–15 for girls and 16–17 for boys), age doesn’t drastically change what your IBW should be. However, as you get older, you naturally lose a bit of height and muscle, making it easier to gain fat. Adopting healthy habits can help counteract these changes.

Gender:
Generally, women weigh less than men even though they have a higher body fat percentage. Men typically have more muscle and denser bones, and they tend to be taller on average, all of which contribute to a higher weight.

Height:
Taller individuals will naturally weigh more because they have more body mass overall—more muscle, more bone, and more fat. For two people of the same height, the one with more muscle (often the man) will typically weigh about 10–20% more.

Body Frame Size:
Your bone structure also plays a role. A person with a larger frame (often determined by measuring wrist circumference relative to height) will usually weigh more than someone with a smaller frame. For example, women and men have specific wrist measurement ranges that classify them as small, medium, or large boned, which can shift their ideal weight.

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Common Formulas for Estimating Ideal Weight

IBW formulas were originally designed for medical dosing and usually start with a base weight for someone who is 5 feet tall, then add extra weight for each additional inch. Here are a few well-known formulas:

• Hamwi 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
• Devine 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
    (This is the most commonly used formula.)
• Robinson Formula (1983):
  • Men: 52 kg + 1.9 kg per inch over 5 feet
  • Women: 49 kg + 1.7 kg per inch over 5 feet
• Miller 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

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The Role of BMI

Another popular measure is the Body Mass Index (BMI), which calculates weight relative to height. The World Health Organization considers a BMI between 18.5 and 25 to be healthy for adults. Although BMI is useful for flagging potential health risks, it is only a rough guide because it doesn’t account for differences in muscle mass or body composition. For children and teens, the CDC recommends maintaining a BMI between the 5th and 85th percentiles based on age.

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Limitations of IBW and Other Formulas

Remember that these formulas are broad estimates designed to apply to a wide range of people. They mainly consider height and gender, without factoring in differences like muscle mass, body composition, physical disabilities, or even lifestyle differences. As a result, your calculated IBW should be seen as a guideline rather than a strict rule. The best indicator of health is not the number on the scale but overall wellness and healthy habits.

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