Ideal Body Weight (IBW) Calculator

Use this Ideal Body Weight calculator to find your estimated healthy weight range based on your height and sex. The calculator implements four validated formulas—Devine, Robinson, Miller, and Hamwi—giving you a range of estimates rather than a single number. Results include BMI-based healthy weight ranges for additional context.

What Is Ideal Body Weight?

Ideal Body Weight (IBW) is a weight reference point based on height and sex, originally developed to help healthcare providers calculate proper medication dosages. Over time, these formulas have been adopted more broadly as general health reference points, though their limitations should be understood.

Unlike BMI which assesses weight relative to height for any individual, IBW formulas attempt to define what someone "should" weigh based on population-level data from specific time periods. This distinction matters because IBW formulas don't account for individual variation in muscle mass, bone density, or ethnic differences in body composition.

Formulas Used in This Calculator

This calculator implements four commonly cited IBW formulas. All use a base weight at 5 feet (152 cm) of height with incremental additions for each inch above that baseline.

1. Devine Formula (1974)

The most widely used formula in clinical settings, particularly for drug dosing calculations. Developed by Dr. B.J. Devine for calculating aminoglycoside antibiotic doses.

Note: The Devine formula was derived empirically rather than from large-scale population studies. Despite limited validation data, it became the standard due to widespread clinical adoption.

2. Robinson Formula (1983)

Developed by Robinson and colleagues as a refinement of the Devine formula, also intended primarily for pharmacokinetic applications.

Characteristics: Generally produces intermediate values between Devine and Miller. The lower increment per inch results in less variation across heights.

3. Miller Formula (1983)

Also published in 1983, the Miller formula tends to produce the highest IBW estimates among the four formulas.

Characteristics: The higher baseline weights but lower increments per inch mean Miller estimates are higher at shorter heights but converge with other formulas at taller heights.

4. Hamwi Formula (1964)

The oldest formula included here, developed by Dr. George Hamwi for use in diabetes management and nutrition counseling. It remains commonly used in dietetics practice.

Characteristics: The higher increment per inch (especially for men) means Hamwi estimates diverge more significantly from other formulas at taller heights.

Frame Size Adjustments

The calculator offers optional frame size adjustments to account for variations in bone structure. Traditional guidance suggests adjusting IBW by ±10% for small or large frames respectively.

Determining Your Frame Size

The wrist circumference method is the most common way to estimate frame size. Wrists are used because they have minimal fat and muscle tissue, making them a reasonable proxy for underlying bone structure.

How to Measure Your Wrist

Using a flexible measuring tape, wrap it around the smallest part of your wrist, just above the prominent wrist bone (the bony bump on the outer side). Keep the tape snug but not tight. Record the measurement in inches.

Frame Size Reference Tables

Compare your wrist measurement against the tables below. Note that women's reference values vary by height, while men's values are consistent for heights over 5'5".

Source: MedlinePlus Medical Encyclopedia

BMI-Based Healthy Weight Range

In addition to IBW formulas, the calculator displays the weight range corresponding to a BMI of 18.5 to 24.9, which the World Health Organization classifies as "normal weight" for adults.

The BMI-based range provides useful context because it's derived from large epidemiological studies linking body weight to health outcomes. However, BMI also has limitations—it doesn't distinguish between muscle and fat mass, and optimal BMI may vary across different populations and age groups.

Limitations of Ideal Body Weight Formulas

IBW formulas have significant limitations that users should understand:

Historical Derivation: Most formulas were developed decades ago from limited population samples, often predominantly white, middle-class Americans. They may not reflect healthy weights for all populations.

No Body Composition Consideration: IBW formulas treat all weight equally, not distinguishing between muscle and fat. An athlete with significant muscle mass may exceed their "ideal" weight while having excellent metabolic health.

Original Purpose Was Medication Dosing: These formulas were designed to estimate lean body mass for drug calculations, not to define health goals. Their adoption as health targets was never their intended use.

Height Limitations: All formulas use 5 feet as a baseline. For heights significantly below this threshold, the formulas produce mathematically questionable results (and may even yield negative values at very short heights).

No Age Consideration: Body composition naturally changes with age, yet IBW formulas produce the same result for a 25-year-old and a 75-year-old of the same height and sex.

Interpreting Your Results

The calculator displays results from all four formulas to show the range of estimates. This range itself is informative—it demonstrates that there is no single "correct" ideal weight, even within these simplified models.

When IBW May Be Useful

Despite limitations, IBW formulas serve legitimate purposes. Healthcare providers use IBW for calculating medication doses, especially for drugs with narrow therapeutic windows. Nutritionists may use IBW as a starting point for estimating caloric needs. Researchers sometimes use IBW to standardize comparisons across study participants.

When to Look Beyond IBW

IBW formulas are less useful for athletes or highly active individuals who carry more muscle mass, older adults whose body composition has changed with age, people from populations not represented in the original formula development, and anyone whose weight differs significantly from IBW but who maintains good metabolic health markers.

For a more comprehensive assessment, consider using our Body Fat Calculator to estimate your body composition, or our TDEE Calculator to understand your energy expenditure based on your actual weight and activity level.

Further Reading:

1. The Devine formula was originally published by B.J. Devine in Drug Intelligence and Clinical Pharmacy (1974) as part of research on gentamicin antibiotic dosing, and later became the most widely used ideal body weight equation in clinical practice.
2. The Robinson formula was developed by J.D. Robinson and colleagues, published in the American Journal of Hospital Pharmacy (1983), as a refined approach to estimating ideal body weight for drug dosage calculations. View study
3. The Miller formula was published by D.R. Miller and colleagues in the American Journal of Hospital Pharmacy (1983), originally developed for determining ideal body weight in the context of digoxin dosing.
4. The Hamwi formula was introduced by G.J. Hamwi in a chapter on dietary therapy within the American Diabetes Association's Diabetes Mellitus: Diagnosis and Treatment (1964), and remains commonly used in dietetics practice.
5. A historical review by M.P. Pai and F.P. Paloucek, published in the Annals of Pharmacotherapy (2000), traced the origins and evolution of the major ideal body weight equations used in clinical practice. View study
6. Research by C.M. Peterson and colleagues, published in The American Journal of Clinical Nutrition (2016), proposed a universal equation for estimating ideal body weight that addresses limitations of the older height-based formulas. View study
7. The BMI-based healthy weight range used in this calculator follows classifications established by the World Health Organization in their Technical Report Series on obesity prevention and management (2000).
8. The frame size reference tables are based on the MedlinePlus Medical Encyclopedia entry on calculating body frame size, maintained by the U.S. National Library of Medicine. View resource