What Is Ideal Body Weight and How Is It Calculated?
Ideal body weight (IBW) refers to the weight range that medical research has associated with the lowest health risks for a person of a given height and gender. Unlike a single magic number, ideal weight is best understood as a range — a zone where your body is statistically most likely to function well and face the fewest weight-related health complications. The concept has been used in clinical medicine since the 1960s, originally developed to help determine drug dosages, assess nutritional status, and set goals for weight management programs.
Several researchers have proposed formulas to estimate ideal body weight, each based on different data sets and assumptions. No single formula is universally accepted as the most accurate, which is why this calculator presents results from five different methods side by side. Looking at the full range across formulas gives you a much more realistic picture than relying on any one equation alone.
The Five Formulas Explained
Devine Formula (1974) — Originally developed by Dr. B.J. Devine for calculating medication dosages, this formula became one of the most widely referenced in clinical practice. It estimates ideal weight based on a baseline at 5 feet of height plus an increment for each additional inch. Despite its widespread use, it is known to underestimate ideal weight for shorter women.
Robinson Formula (1983) — Created by Dr. J.D. Robinson and colleagues, this formula was designed as a refinement of the Devine equation. It uses different increments per inch for men and women and is considered a more balanced estimate across a range of heights.
Miller Formula (1983) — Dr. D.R. Miller proposed this formula in the same year as Robinson's, using slightly different coefficients. It tends to produce higher ideal weight estimates, particularly for taller individuals, and is sometimes seen as more lenient than Devine or Robinson.
Hamwi Formula (1964) — One of the earliest ideal weight formulas, proposed by Dr. G.J. Hamwi. It uses larger per-inch increments and tends to produce a wider spread between short and tall individuals. It remains popular in dietetics and clinical nutrition practice.
Healthy BMI Range (18.5–24.9) — Rather than a named formula, this method calculates the weight range corresponding to a BMI between 18.5 and 24.9, which the World Health Organization considers normal. It provides the broadest range and serves as a useful sanity check against the other formulas.
How Frame Size Affects Your Results
Body frame size reflects skeletal structure — people with wider shoulders and larger wrists naturally weigh more at the same height. The standard adjustment is roughly 10 percent: a small frame subtracts 10% from the base estimate, while a large frame adds 10%. If you're unsure of your frame size, wrapping your thumb and middle finger around your wrist is a common quick test. If they overlap, you likely have a small frame; if they just touch, medium; and if they don't meet, large.
Limitations to Keep in Mind
All ideal weight formulas share important limitations. They were derived from population averages, primarily from data collected on Caucasian adults, and may not apply equally across all ethnic backgrounds. They do not distinguish between lean mass and fat mass — a muscular person may exceed their "ideal" weight while being in excellent health. Athletes, pregnant women, older adults, and anyone with a chronic health condition should interpret these numbers with extra caution and consult their healthcare provider.
These formulas also require a minimum height of 5 feet (152 cm). For individuals shorter than this threshold, the linear extrapolations used by these equations become unreliable.
Frequently Asked Questions
What is ideal body weight?
Ideal body weight is a statistical estimate of the weight range associated with the lowest health risks for a given height, gender, and frame size. It is not a single definitive number but a range derived from decades of population-level research.
Which ideal weight formula is most accurate?
No single formula is universally most accurate. The Devine formula is the most commonly cited in clinical settings, but Robinson and Miller are considered more modern refinements. Comparing results from all formulas — as this tool does — gives the most useful picture.
Does frame size really matter?
Yes. Skeletal structure varies significantly between individuals. Someone with a large frame will naturally weigh more at a given height without any excess body fat. The 10% adjustment is a simplified but widely used correction.
Are these formulas valid for all heights?
These formulas were developed for adults 5 feet (152 cm) and taller. Results for shorter individuals may be unreliable. They also do not apply to children or adolescents, whose ideal weight depends on age-specific growth charts.
Should I use ideal weight as a goal?
Ideal weight formulas can be a helpful reference point, but they should not be your sole target. Overall health depends on many factors including body composition, fitness level, blood markers, and mental wellbeing. Use these estimates as one data point among many.
This ideal weight calculator is completely free, runs entirely in your browser, and stores nothing on a server. Bookmark this page to check your ideal weight anytime — quick, private, and instant.