Ideal Weight Calculator
Calculate ideal body weight using Devine, Robinson, Miller, and Hamwi formulas.
What Is the Ideal Weight Calculator?
Ideal Body Weight (IBW) formulas were developed primarily for clinical use, calculating medication dosages, ventilator settings, and nutritional requirements that scale better with lean body mass than total body weight. Each formula was developed by a different researcher for a different clinical population, which is why their results differ slightly.
- ›All four formulas: the calculator computes Devine, Robinson, Miller, and Hamwi simultaneously so you can compare them side by side.
- ›Height inputs: accepts feet/inches or centimeters; converts internally to the formula's inch-based system.
- ›Gender selection: male and female formulas have different base weights and per-inch increments.
- ›Current weight comparison: enter your actual weight to see the difference from IBW and a percentage-above/below indicator.
- ›BMI cross-reference: the tool also shows your BMI category alongside IBW, as the two measures complement each other.
- ›Not a medical prescription: IBW formulas are approximations for reference, individual body composition, age, and health status matter more.
Formula
| Formula | Male (kg) | Female (kg) |
|---|---|---|
| Devine (1974) | 50 + 2.3 × (H − 60) | 45.5 + 2.3 × (H − 60) |
| Robinson (1983) | 52 + 1.9 × (H − 60) | 49 + 1.7 × (H − 60) |
| Miller (1983) | 56.2 + 1.41 × (H − 60) | 53.1 + 1.36 × (H − 60) |
| Hamwi (1964) | 48 + 2.7 × (H − 60) | 45.4 + 2.2 × (H − 60) |
How to Use
- 1Select your biological sex (male or female), the formulas have sex-specific base weights.
- 2Enter your height in feet + inches or switch to centimeters. Heights above 5 ft (152 cm) use the incremental formula; shorter heights use the base weight.
- 3Optionally enter your current weight in kg or lb to see how you compare to the IBW range.
- 4Press Calculate (or hit Enter) to see all four IBW values, the average, and your BMI if current weight is provided.
- 5Use the preset height buttons (5'6", 5'10", 6'0") for quick reference values.
- 6Toggle between metric (kg/cm) and imperial (lb/ft·in) using the unit selector.
- 7Click Reset (or Escape) to clear and start over.
Example Calculation
Example, Male, 5 ft 10 in (178 cm)
Height = 70 inches → (H − 60) = 10
Example, Female, 5 ft 4 in (163 cm)
Height = 64 inches → (H − 60) = 4
Understanding Ideal Weight
What Is Ideal Body Weight?
Ideal Body Weight (IBW) is a clinical concept that estimates the body weight at which a person of a given height and sex is expected to have optimal health outcomes, particularly for pharmacokinetic drug dosing and respiratory mechanics. These formulas emerged in the 1960s–1980s from studies on drug metabolism and are still widely used in ICUs and pharmacy dosing guidelines.
IBW is not a definition of "perfect" or "attractive" weight, it is a medical approximation based on population data. People with high muscle mass (athletes, bodybuilders) will legitimately weigh more than their IBW, while people with low muscle mass may be at IBW despite having high body fat percentage. Body composition matters more than any single number.
How the Four Formulas Differ
- ›Devine (1974), developed for creatinine clearance estimation and is the most widely cited formula. Most drug dosing guidelines that reference IBW are based on Devine.
- ›Robinson (1983), a modification of Devine with slightly different coefficients derived from an NHANES dataset. Gives results very close to Devine for most heights.
- ›Miller (1983), developed from a larger NHANES dataset, produces higher base weights and smaller per-inch increments. Often the highest estimate for shorter individuals and lowest for taller ones.
- ›Hamwi (1964), one of the oldest formulas, commonly used by registered dietitians for nutritional assessment. Uses 48 kg (male) and 45.4 kg (female) as base for 5 ft with a steeper per-inch increment of 2.7 kg (male).
IBW vs BMI vs Body Fat Percentage
Each measure captures a different aspect of body weight:
- ›IBW, a height-based formula giving a single target weight; primarily for clinical/pharmacological use.
- ›BMI (Body Mass Index), weight divided by height squared; a population-level screening tool. Doesn't distinguish muscle from fat.
- ›Body fat percentage, the gold standard for body composition, but requires measurement tools (DEXA scan, bioimpedance, caliper test).
- ›Adjusted Body Weight (AdjBW), used when actual weight >130% of IBW: AdjBW = IBW + 0.4 × (actual − IBW). Used for drug dosing in obesity.
Clinical Uses of IBW
- ›Drug dosing: many renally-cleared medications (aminoglycosides, vancomycin) are dosed by IBW or adjusted body weight, not actual weight, overdosing obese patients would cause toxicity.
- ›Mechanical ventilation: tidal volume settings in ICU ventilators are based on IBW (6–8 mL/kg IBW) to prevent ventilator-induced lung injury.
- ›Nutritional support: caloric requirements are sometimes estimated per kg IBW rather than actual weight to avoid overfeeding.
- ›Fitness goals: IBW gives an evidence-based reference range for those seeking general health guidance, though individual targets should be set with a clinician.
Frequently Asked Questions
Which IBW formula is most accurate?
No single formula is universally most accurate, they were each derived from different datasets and intended for different clinical purposes.
- ›Devine (1974), most widely referenced in drug dosing literature; default in most pharmacy protocols
- ›Hamwi (1964), commonly used for nutritional assessment by dietitians
- ›Robinson (1983), close to Devine, derived from a larger NHANES dataset
- ›Miller (1983), tends to be highest for shorter individuals, lowest for very tall
For practical purposes, looking at all four and using the average or a range gives better insight than relying on any single formula.
Is it possible to be "above" IBW and still be healthy?
Absolutely. Athletes and people with significant muscle mass routinely weigh 10–20% above IBW while having excellent health markers.
IBW was not designed to define optimal fitness or aesthetics, it was designed as a simple clinical proxy for drug dosing and ventilator settings. Body fat percentage, blood markers, cardiovascular fitness, and metabolic health are far better indicators of overall health than any single weight number.
Why do the male and female formulas have different starting weights?
Men and women at the same height have different average lean body mass due to physiological differences:
- ›Men generally have greater bone density and skeletal mass per inch of height
- ›Men have a higher proportion of muscle mass relative to total body weight
- ›These differences are reflected in the higher male base weights (e.g., Devine: 50 kg male vs 45.5 kg female at 5 ft)
The per-inch increment above 5 ft also differs slightly between sexes in some formulas, reflecting different rates of height-related lean mass accumulation.
How does IBW apply to children?
The standard IBW formulas (Devine, Robinson, Miller, Hamwi) were developed for adults and should NOT be used for children or adolescents.
Pediatric ideal weight is assessed using weight-for-age and weight-for-height percentiles from growth charts (CDC or WHO), which account for normal developmental variation across age groups. A child's "healthy weight" changes significantly year by year as they grow.
What is Adjusted Body Weight (AdjBW) and when is it used?
AdjBW = IBW + 0.4 × (Actual Body Weight − IBW). It is used when a patient's actual weight exceeds 130% of their IBW (clinically obese).
Because adipose tissue has some metabolically active mass, but far less than lean tissue, AdjBW provides a middle ground between IBW and actual weight for drug dosing calculations. Using actual weight in obese patients can cause toxicity; using IBW can underdose.
Many ICU pharmacokinetics protocols specify whether to use IBW, AdjBW, or actual body weight depending on the drug. Always verify with a clinical pharmacist.
What if my height is under 5 feet?
The IBW formulas are designed for adults taller than 5 feet (152 cm). For heights at or below 5 feet, the formulas return the base weight without any per-inch adjustment.
- ›Devine male base: 50 kg at 5 ft
- ›Devine female base: 45.5 kg at 5 ft
- ›Some clinicians subtract 2 kg per inch below 5 ft, but this is not standardized
For dosing decisions in very short patients, consult a clinical pharmacist rather than relying on the standard formulas alone.
Does ethnicity or age affect ideal weight?
The standard IBW formulas do not account for ethnicity or age, but research suggests these factors matter clinically.
- ›Asian populations tend to have higher body fat at the same BMI, some guidelines use lower cutoffs (BMI 23 vs 25) for Asian patients
- ›Older adults lose muscle mass (sarcopenia), IBW may overestimate lean mass in elderly patients
- ›Adjusted equations for specific populations are used in specialized clinical settings
For standard reference purposes the formulas are acceptable, but clinical dosing in these groups should involve specialist review.