Ideal Weight Calculator
See what multiple clinical formulas say about ideal body weight for your height and sex, alongside the NHS BMI healthy weight range.
How Ideal Weight Calculator works
Clinical ideal weight formulas
Ideal body weight (IBW) formulas were originally developed for pharmacological dosing — many drug doses were calculated as mg/kg of ideal rather than actual weight. The Devine formula (1974) is the most widely used: 50 kg + 2.3 kg for each inch above 5 feet for men; 45.5 kg + 2.3 kg for women. The Robinson (1983) and Miller (1983) formulas were proposed as refinements but all three give similar results for average heights.
BMI healthy weight range
The BMI healthy range (18.5–24.9) translated into absolute weight depends on height: weight = BMI × height². For a 5'9" (175 cm) man, the healthy BMI range corresponds to roughly 57–76 kg. This range is broader than any single IBW formula and is more appropriate as a health reference than a single target weight.
Why "ideal weight" is a problematic concept
These formulas were derived from insurance actuarial data collected in the 1940s–1960s from primarily white, North American populations. They do not account for muscle mass, bone density, body composition, ethnicity, or frame size. An athlete with high muscle mass may weigh significantly more than their "ideal weight" while being in excellent health. The term "ideal" weight is increasingly avoided in clinical practice in favour of "healthy weight range".
What to do with this information
If your current weight is within the BMI healthy range for your height, there is generally no medical reason to target a lower weight. If you are above the range, weight management may reduce health risks — though body composition and waist circumference are also important indicators. Focus on sustainable lifestyle changes rather than achieving a specific number. A GP or dietitian can provide context specific to your health situation.
Frequently asked questions
What is a healthy weight for my height?
The NHS defines a healthy weight as having a BMI of 18.5–24.9. For a 5'6" (168 cm) woman, this is approximately 52–70 kg (8 st 3 lb – 11 st 0 lb). This calculator shows the range and also single-point estimates from three clinical formulas.
Which ideal weight formula is most accurate?
No single formula is universally "most accurate" because body composition varies enormously. The Devine formula is the most commonly used in clinical settings for drug dosing. The BMI healthy range is the most evidence-based reference for health risk assessment. For most purposes, treat these as a broad reference range rather than a precise target.
Should I aim to be at the bottom of the BMI healthy range?
Not necessarily. Within the healthy BMI range (18.5–24.9), there is no established correlation between being at the lower versus higher end and health outcomes for most people. Individual factors like muscle mass, age, and fitness level matter more than exact weight within the healthy range.
I'm below my "ideal weight" — is this a problem?
Being underweight (BMI below 18.5) can indicate malnutrition or underlying health issues and carries its own health risks including bone density loss, immune function impairment, and fertility effects. If you are consistently below the healthy BMI range, speak to a GP.
This calculator provides estimates for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.