What Ideal Body Weight Means and Why the Math Matters

Ideal body weight is a target range based on your height, age, and sex—calculated using medical formulas that doctors and nutritionists have used for decades. It is not a single magic number, but rather a range that accounts for differences in bone density, muscle mass, and body composition. The formulas give you a starting point for conversations with your doctor about whether your current weight supports your health.

These calculations are useful because they let you compare yourself to a standard rather than guessing. They also help you track progress if you are working with a trainer or doctor on weight management. The most common formulas—the Devine formula and the Hamwi formula—were developed by pharmacists to calculate medication dosages, which is why they remain reliable: they had to work in real medical settings.

Keep in mind that ideal body weight is not the same as a healthy weight for you specifically. Your actual healthy range depends on your fitness level, muscle mass, bone structure, and medical history. These formulas give you a reference point, not a diagnosis.

Key Takeaways

  • The Devine formula and Hamwi formula are the two most widely used methods, and both require only your height and sex to calculate a target range.
  • The Devine formula starts with a base weight for your height and adds or subtracts pounds for each inch above or below 5 feet.
  • The Hamwi formula uses a similar step method but produces slightly different numbers, so using both gives you a realistic range rather than a single target.
  • Your actual ideal weight depends on your age, fitness level, and body composition, so these formulas work best as a conversation starter with your doctor.
  • Frame size—whether you have a small, medium, or large bone structure—can shift your target range by 10 to 15 pounds in either direction.

The Devine Formula: Step-by-Step Calculation

The Devine formula, created in 1974, is the most commonly cited method in medical literature. It works by establishing a base weight for someone 5 feet tall, then adding or subtracting a fixed amount for each inch of height above or below that baseline.

For men, the formula is: 50 kg (110 pounds) for the first 5 feet, plus 2.3 kg (5 pounds) for each inch over 5 feet. If you are a man who is 5 feet 10 inches tall, you would calculate it this way: 110 pounds plus (10 inches × 5 pounds) = 110 + 50 = 160 pounds. That 160 pounds is your baseline ideal body weight using the Devine method.

For women, the formula is: 45.5 kg (100 pounds) for the first 5 feet, plus 2.3 kg (5 pounds) for each inch over 5 feet. A woman who is 5 feet 6 inches tall would calculate: 100 pounds plus (6 inches × 5 pounds) = 100 + 30 = 130 pounds. Again, this is your baseline using the Devine formula.

The Devine formula produces a single number, not a range. Most doctors add a 10 percent buffer on either side to account for frame size and individual variation. So a man with a Devine result of 160 pounds would have a realistic range of roughly 144 to 176 pounds.

The Hamwi Formula: An Alternative Calculation

The Hamwi formula, developed around the same time as the Devine formula, uses the same step method but with slightly different base weights and increments. It tends to produce results that are 5 to 10 pounds higher than the Devine formula, which is why many health professionals use both to establish a range.

For men, the Hamwi formula is: 48 kg (106 pounds) for the first 5 feet, plus 2.7 kg (6 pounds) for each inch over 5 feet. The same 5-foot-10-inch man would calculate: 106 pounds plus (10 inches × 6 pounds) = 106 + 60 = 166 pounds. Notice this is 6 pounds higher than the Devine result of 160 pounds.

For women, the Hamwi formula is: 45.5 kg (100 pounds) for the first 5 feet, plus 2.7 kg (6 pounds) for each inch over 5 feet. A 5-foot-6-inch woman would calculate: 100 pounds plus (6 inches × 6 pounds) = 100 + 36 = 136 pounds. This is 6 pounds higher than her Devine result of 130 pounds.

Using both formulas gives you a band rather than a single target. The 5-foot-10-inch man has a Devine result of 160 and a Hamwi result of 166, so his calculated range is 160 to 166 pounds before adjusting for frame size.

Adjusting for Frame Size

Neither the Devine nor Hamwi formula accounts for bone structure, which can shift your ideal weight by 10 to 15 pounds. A person with a large frame naturally weighs more; a person with a small frame weighs less. You can estimate your frame size using a straightforward wrist measurement.

Measure the circumference of your wrist just below the wrist bone, where it is narrowest. For men: a wrist circumference under 6.5 inches suggests a small frame, 6.5 to 7.5 inches is medium, and over 7.5 inches is large. For women: under 5.5 inches is small, 5.5 to 6.3 inches is medium, and over 6.3 inches is large.

Once you know your frame size, adjust your calculated ideal weight. For a small frame, subtract 10 percent from your result. For a large frame, add 10 percent. A 5-foot-10-inch man with a Devine result of 160 pounds and a large frame would adjust to 160 × 1.10 = 176 pounds as his upper target. A woman with the same Devine result of 130 pounds and a small frame would adjust to 130 × 0.90 = 117 pounds as her lower target.

Why These Formulas Have Limits

The Devine and Hamwi formulas were created to calculate medication dosages, not to define health. They do not account for age, fitness level, muscle mass, or medical conditions. A 25-year-old athlete and a 65-year-old with arthritis might have the same height and sex but very different healthy weight ranges.

Muscle weighs more than fat, so someone who lifts weights regularly may weigh more than the formula suggests while still being in excellent health. Conversely, someone who is sedentary may weigh less than the formula suggests but have poor cardiovascular fitness. The formulas are useful as a reference point, not as a medical judgment.

Age also matters. Research shows that people over 65 often have better health outcomes at weights slightly above the calculated ideal, possibly because some extra weight protects against falls and illness. Your doctor can tell you whether your target should shift based on your age and medical history.

Using Your Calculated Weight in Conversation with Your Doctor

Once you have calculated your ideal body weight using both formulas and adjusted for frame size, you have a range to discuss with your doctor. Bring your calculations with you and explain which formula you used. Your doctor can then tell you whether that range makes sense for your specific situation—your age, fitness level, medications, and any chronic conditions.

Your doctor may suggest a target that is higher or lower than the formula predicts, and that is normal. The formulas are a starting point, not a prescription. If you are working toward a weight change, your doctor can also help you set a realistic timeline and identify whether diet, exercise, medical treatment, or a combination is the right approach for you.

Keep in mind that weight is only one measure of health. Blood pressure, cholesterol, blood sugar, fitness level, and how you feel day to day all matter. A number on the scale is useful information, but it is not the whole picture.

Frequently Asked Questions

Should I use the Devine or Hamwi formula?

Both are equally valid. The Devine formula is cited more often in medical literature, but the Hamwi formula is also widely used. Using both gives you a realistic range rather than relying on a single number. Most health professionals recommend calculating with both and then adjusting for your frame size.

What if I am under 5 feet tall or over 6 feet 6 inches?

The formulas work best for people between 5 feet and 6 feet 6 inches. Outside that range, the formulas become less reliable because the step increments do not scale the same way. If you are significantly shorter or taller, ask your doctor for a personalized target rather than relying on the formula alone.

Do these formulas work for children and teenagers?

No. The Devine and Hamwi formulas were designed for adults and do not account for growth and development. Children and teenagers should work with their pediatrician to determine a healthy weight range based on growth charts and their individual development.

How often should I recalculate my ideal body weight?

Your ideal weight does not change unless your height changes, which is rare in adults. You only need to calculate it once. However, your actual healthy weight may shift as you age or your fitness level changes, so check in with your doctor every few years about whether your target range still makes sense.

Can I use these formulas if I am pregnant or breastfeeding?

No. Pregnancy and breastfeeding change your body composition and caloric needs significantly. Talk to your obstetrician or midwife about a healthy weight range during and after pregnancy rather than using these general formulas.