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What Is Ideal Body Weight and How Is It Calculated?
Ideal body weight is a widely used clinical benchmark but it is often misunderstood and misapplied. Here is what the formulas actually measure, how to calculate them, and what they do and do not tell you about health.
ToolSpot AI Team
Editorial
July 3, 20265 min read
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What Is Ideal Body Weight and How Is It Calculated?
Ideal body weight is one of those health concepts that sounds simple but becomes more complicated on examination. There are multiple competing formulas, none of which account for body composition, and most of which were originally developed for clinical drug dosing rather than personal health goals.
This guide explains what ideal body weight actually measures, walks through the most widely used formulas, and puts the concept in context alongside other health metrics.
What is ideal body weight?
Ideal body weight (IBW) is an estimated weight range considered appropriate for a given height. It is used clinically to:
Calculate appropriate drug dosages (many medications are dosed based on IBW rather than actual weight)
Estimate lung function baselines
Assess nutritional status in clinical settings
Set weight targets in obesity treatment programmes
IBW is not a definitive measure of health. It does not distinguish between muscle and fat, does not account for age, ethnicity, or body composition, and was originally derived from population data collected on insurance applicants in the mid-20th century - not from direct health outcome research.
The main IBW formulas
Several formulas are used in clinical and fitness contexts. The most widely referenced are:
Devine formula (1974) - the most commonly used in clinical medicine:
For men: IBW (kg) = 50 + 2.3 x (height in inches above 5 feet)
For women: IBW (kg) = 45.5 + 2.3 x (height in inches above 5 feet)
Example for a 5 foot 9 inch (69 inch) man:
IBW = 50 + 2.3 x (69 minus 60) = 50 + 2.3 x 9 = 50 + 20.7 = 70.7 kg (approximately 156 pounds)
Example for a 5 foot 5 inch (65 inch) woman:
IBW = 45.5 + 2.3 x (65 minus 60) = 45.5 + 11.5 = 57 kg (approximately 126 pounds)
Robinson formula (1983):
For men: IBW (kg) = 52 + 1.9 x (height in inches above 5 feet)
For women: IBW (kg) = 49 + 1.7 x (height in inches above 5 feet)
Miller formula (1983):
For men: IBW (kg) = 56.2 + 1.41 x (height in inches above 5 feet)
For women: IBW (kg) = 53.1 + 1.36 x (height in inches above 5 feet)
Hamwi formula (1964) - commonly used by dietitians:
For men: IBW (pounds) = 106 + 6 x (height in inches above 5 feet)
For women: IBW (pounds) = 100 + 5 x (height in inches above 5 feet)
The different formulas produce somewhat different results for the same person. This reflects the fact that there is no single scientifically validated correct answer - these are all approximations from historical population data.
IBW vs healthy weight range
A single ideal weight number implies more precision than is warranted. In practice a healthy weight range is more clinically meaningful.
Most healthcare providers use BMI to define healthy weight ranges:
BMI 18.5 to 24.9 is classified as healthy weight for most adults. Converting this BMI range to weight for a given height gives a range rather than a single number.
For a 5 foot 9 inch (175cm) person:
BMI 18.5 corresponds to approximately 125 pounds (57 kg)
BMI 24.9 corresponds to approximately 168 pounds (76 kg)
Healthy weight range: approximately 125 to 168 pounds
This range is more practical than a single IBW figure because it acknowledges natural variation in healthy body composition.
Limitations of ideal body weight
Does not account for muscle mass - athletes and muscular individuals are frequently classified as overweight by IBW and BMI standards despite having low body fat and excellent health markers.
Does not account for age - older adults naturally lose muscle mass. A weight that is ideal at 30 may be too low at 70 if it means inadequate muscle mass for strength and fall prevention.
Does not account for ethnicity - research has shown that metabolic health risks occur at lower BMI and weight thresholds for people of Asian descent compared to European populations. Standard IBW formulas may overestimate ideal weight for some populations.
Originally developed for drug dosing - the Devine formula was created to estimate appropriate aminoglycoside antibiotic dosing, not to define health goals. Its widespread adoption in fitness contexts goes well beyond its original intent.
Binary sex assumption - all the standard formulas use a binary male/female classification which does not reflect the full range of human biology.
Better measures to use alongside IBW
Body fat percentage - directly measures the ratio of fat to lean mass, which is what actually matters for metabolic health. Can be measured through DEXA scan, hydrostatic weighing, or estimated via Navy circumference method.
Waist circumference - abdominal fat is more closely linked to cardiovascular and metabolic risk than total weight. A waist above 94cm (37 inches) for men or 80cm (31.5 inches) for women indicates elevated risk by most guidelines.
Waist-to-height ratio - many researchers consider this a better predictor of metabolic risk than either BMI or IBW. A ratio below 0.5 (waist circumference less than half your height) is generally associated with lower risk.
Blood markers - cholesterol, blood glucose, blood pressure, and inflammatory markers provide a far more complete picture of metabolic health than any weight-based measure.
Practical use of ideal body weight
IBW is most useful as a starting point or rough benchmark rather than a fixed target. If your weight is significantly above your IBW range (40% or more above) it may indicate excess body fat worth addressing for health reasons. If you are within the healthy BMI range and have good metabolic markers, hitting a specific IBW number is not a meaningful health goal.
For personal fitness goals, focus on body composition - reducing fat and maintaining or building muscle - rather than on the scale weight matching a formula-derived number.
Try the free calculators
Use ToolSpotAI's free Ideal Weight Calculator to see your IBW estimates across multiple formulas. The BMI Calculator shows your current BMI and healthy weight range for your height.
No signup required. Everything runs in your browser.
Related tools on ToolSpotAI
Ideal Weight Calculator
BMI Calculator
Body Fat Calculator
Calorie and TDEE Calculator
BMR Calculator
Frequently asked questions
No single formula is definitively most accurate - they are all approximations from different historical datasets. The Devine formula is most commonly used in clinical medicine for drug dosing. The Hamwi formula is popular among dietitians. For personal health purposes a healthy BMI range (18.5 to 24.9) combined with waist circumference measurement provides a more complete picture than any single IBW formula.
Not exactly. IBW formulas produce a single number while healthy weight is better understood as a range. The healthy BMI range of 18.5 to 24.9 typically encompasses the IBW estimates from most formulas. IBW also does not account for body composition - a person can be at their IBW but have an unhealthy ratio of fat to muscle.
Most standard IBW formulas become unreliable below 5 feet in height because they were derived from populations with limited representation of shorter adults. For people under 5 feet, BMI-based healthy weight ranges are generally more appropriate, though even these have limitations. Consult a healthcare provider for personalised guidance.
The IBW formulas do not change with age since they are based solely on height. However what constitutes a healthy weight in practice may shift with age - particularly in older adults where maintaining muscle mass becomes more important and some additional weight may be associated with better outcomes. Standard IBW formulas should be interpreted with age in mind.
The most important clinical use of IBW is medication dosing. Many drugs - particularly antibiotics, anaesthetic agents, and chemotherapy - are dosed based on IBW rather than actual body weight because the drug distributes through lean tissue rather than fat. Using actual weight for these medications in obese patients would result in overdosing.
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