Ideal Body Weight: How to Calculate Your Target Weight (5 Formulas)

What Is Ideal Body Weight (IBW)?

Ideal Body Weight (IBW) is an estimate of the healthiest weight for a person based on their height. IBW was originally developed in the 1960s-1980s to help doctors calculate appropriate medication dosages, since drug metabolism is more closely related to lean body mass than total body weight.

Today, IBW is used for multiple purposes:

• Medical dosing: Calculating medication amounts for anesthesia, chemotherapy, and other drugs
• Health assessment: Estimating a healthy target weight for height
• Sports classification: Many sports categorize athletes by weight classes
• Nutrition planning: Setting calorie and protein targets based on ideal weight
• Weight loss goals: Providing a target weight range for people trying to lose weight

Important limitations of IBW:

• IBW does not account for muscle mass (athletes may exceed IBW and be very healthy)
• IBW does not account for body fat percentage (two people at same IBW can have very different body composition)
• IBW does not account for frame size (though it can be adjusted)
• IBW is not a perfect measure of health — it's just one reference point

How to Calculate Ideal Body Weight: 5 Formulas

There are 5 main formulas for calculating IBW. All use the same format: a base weight at 5 feet tall, plus a set amount per inch over 5 feet. The formulas differ in the specific values used.

1. Hamwi Formula (1964)

The Hamwi formula was developed in 1964 for calculating medication dosages. It's one of the simplest and most conservative formulas.

For men: 106 lbs for 5 feet + 6 lbs per inch over 5 feet

For women: 100 lbs for 5 feet + 5 lbs per inch over 5 feet

Example (5'5" woman):

1. Height over 5 feet: 5 inches
2. IBW = 100 + (5 × 5) = 100 + 25 = 125 lbs

2. Devine Formula (1974) — Most Widely Used

The Devine formula is the most commonly used IBW formula in medical settings. It was developed in 1974 and has become the standard for medication dosing.

For men: 50 kg (110 lbs) for 5 feet + 2.3 kg (5.1 lbs) per inch over 5 feet

For women: 45.5 kg (100 lbs) for 5 feet + 2.3 kg (5.1 lbs) per inch over 5 feet

Example (5'10" man):

1. Height over 5 feet: 10 inches
2. IBW = 50 kg + (2.3 × 10) = 50 + 23 = 73 kg
3. Convert to pounds: 73 × 2.2 = 161 lbs

3. Robinson Formula (1983)

The Robinson formula is a modification of the Devine formula, developed in 1983. It tends to give slightly higher weights.

For men: 52 kg (115 lbs) for 5 feet + 1.9 kg (4.2 lbs) per inch over 5 feet

For women: 49 kg (108 lbs) for 5 feet + 1.7 kg (3.7 lbs) per inch over 5 feet

4. Miller Formula (1983)

The Miller formula is another modification of the Devine formula from 1983. It gives the highest IBW estimates.

For men: 56.2 kg (124 lbs) for 5 feet + 1.41 kg (3.1 lbs) per inch over 5 feet

For women: 53.1 kg (117 lbs) for 5 feet + 1.36 kg (3.0 lbs) per inch over 5 feet

5. BMI-Based Healthy Weight Range

Instead of a single number, you can calculate a healthy weight range based on BMI 18.5-24.9:

Formula:

• Minimum healthy weight = 18.5 × (height in meters)²
• Maximum healthy weight = 24.9 × (height in meters)²

Example (5'5" = 1.65 m):

• Min: 18.5 × (1.65)² = 18.5 × 2.72 = 50.3 kg = 111 lbs
• Max: 24.9 × (1.65)² = 24.9 × 2.72 = 67.7 kg = 149 lbs
• Healthy range: 111-149 lbs

IBW Comparison: All 5 Formulas Side-by-Side

Here's how the different formulas compare for common heights:

IBW for Women by Height

IBW for Men by Height

Adjusting IBW for Frame Size

Body frame size significantly affects your ideal weight. A large-framed person naturally weighs more than a small-framed person at the same height due to bone density and structure.

How to Determine Your Frame Size

Measure your wrist circumference at the smallest point (just below the wrist bone), then compare to your height:

For Women:

For Men:

Adjusting IBW for Frame Size

Once you know your frame size, adjust your IBW:

• Small frame: Subtract 10% from IBW
• Medium frame: Use IBW as calculated
• Large frame: Add 10% to IBW

Example (5'5" woman, IBW = 125 lbs):

• Small frame: 125 - 12.5 = 113 lbs
• Medium frame: 125 lbs
• Large frame: 125 + 12.5 = 138 lbs

IBW vs. BMI: What's the Difference?

IBW and BMI are both tools for assessing healthy weight, but they work differently:

Key differences:

• IBW gives a single number, BMI gives a category (underweight, normal, overweight, obese)
• IBW accounts for gender, BMI uses the same formula for men and women
• IBW can be adjusted for frame size, BMI cannot
• Neither accounts for muscle mass or body composition

Which is better? Use both. Calculate your IBW to get a target weight, then check if that weight falls within the healthy BMI range (18.5-24.9). Your ideal weight is likely somewhere in the overlap.

When IBW Doesn't Apply

IBW formulas have important limitations. They don't work well for:

1. Athletes and Muscular Individuals

Muscle weighs more than fat, so people with high muscle mass often exceed their IBW despite being very healthy.

• Bodybuilders: May weigh 20-50 lbs over IBW with body fat <10%
• Athletes: Football players, rugby players often weigh 30-40 lbs over IBW
• Regular lifters: People who strength train 3-5x/week may weigh 10-20 lbs over IBW

Better metric for athletes: Body fat percentage (men: 6-17%, women: 14-24% for athletes)

2. Older Adults (65+)

Older adults lose muscle mass with age, so IBW may underestimate healthy weight. Being slightly above IBW (but within healthy BMI range) may be protective against frailty.

3. Very Tall or Very Short People

IBW formulas were developed using average heights (5'4"-6'0"). They may be less accurate for people under 5'0" or over 6'4".

4. Pregnant or Breastfeeding Women

Pregnancy weight gain is normal and necessary. IBW doesn't apply during pregnancy or while breastfeeding.

How to Use IBW for Weight Loss Goals

If you're trying to lose weight, IBW can help you set a realistic target. Here's how to use it:

1. Calculate your IBW using multiple formulas (Hamwi, Devine, Robinson, Miller)
2. Calculate your healthy BMI range (18.5-24.9 for your height)
3. Adjust for frame size if you know you're small or large-framed
4. Set a target range, not a single number (e.g., 120-135 lbs instead of exactly 125 lbs)
5. Consider your history: What weight did you feel best at as a healthy adult?
6. Aim for the higher end if you: Exercise regularly, have muscle mass, are over 50
7. Aim for the lower end if you: Are sedentary, have small frame, are under 40

Example goal-setting (5'5" woman, current weight 180 lbs):

• IBW formulas: 120-132 lbs
• Healthy BMI range: 111-149 lbs
• Frame size: Medium
• Activity level: Moderate exercise 3x/week
• Target range: 125-140 lbs (middle of IBW range to upper BMI range)

Beyond IBW: Other Important Health Markers

IBW is just one tool. These markers are equally or more important for health:

1. Waist Circumference

Waist circumference measures abdominal fat, which is more dangerous than fat elsewhere.

• High risk: Men >40 inches, Women >35 inches
• Very high risk: Men >47 inches, Women >43 inches

2. Body Fat Percentage

3. Metabolic Health

• Blood pressure <120/80 mmHg
• Fasting blood sugar <100 mg/dL
• Triglycerides <150 mg/dL
• HDL cholesterol >40 mg/dL (men), >50 mg/dL (women)

4. Fitness Level

Research shows that fitness matters more than fatness. A fit person at IBW + 20 lbs is healthier than an unfit person at exact IBW.

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