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.
Reviewed by Richard Ross · Last updated April 2026
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.
Is there a single "ideal" weight for everyone at a given height?
No. Ideal weight ranges are statistical averages — they represent weights associated with the lowest health risks in population studies. Within any height, there is considerable variation due to bone density, muscle mass, sex, and age. A muscular 5'10" man and a slight 5'10" woman will have different healthy weights. Ideal weight formulas like Robinson, Miller, and Devine provide rough benchmarks, not precise targets. Body composition (fat percentage and muscle mass) matters more than scale weight alone.
What formula does this calculator use?
Ideal weight calculators typically use one of several formulas. The Devine formula (1974) gives 50kg for men + 2.3kg per inch above 5 feet (45.5kg base for women). The Robinson formula (1983) adjusts slightly: 52kg for men + 1.9kg per inch. The Miller formula (1983): 56.2kg + 1.41kg per inch. These were developed for medical dosing and do not account for muscle mass or bone density. BMI-based ideal weight (targeting BMI 21.7, the midpoint of normal) is another common approach.
How does body weight change with age?
Adults tend to gain weight from their 30s to 60s, even with stable activity levels, due to hormonal changes, sarcopenia (muscle loss), and reduced basal metabolic rate. After 65-70, weight often begins to decline naturally. The BMI range associated with lowest mortality shifts slightly upward in older adults — BMI 23-27 may be optimal for those over 65, compared to 20-25 for younger adults. Maintaining muscle mass through resistance exercise is more important for health in older age than matching a specific weight on a scale.
Is it possible to be "normal weight but metabolically obese"?
Yes. "Normal weight obesity" (NWO) — also called thin-fat or TOFI (thin outside, fat inside) — describes people within a healthy BMI range who have high visceral fat and metabolic dysfunction. This is more common in certain ethnic groups (South Asians, in particular) and in people with low muscle mass ("skinny fat"). NWO is associated with insulin resistance, type 2 diabetes, and cardiovascular risk despite a normal BMI. Body fat percentage and waist circumference detect these individuals better than BMI or ideal weight.
How does ideal weight relate to achieving it safely?
Safe weight loss is generally recommended at 0.5-1kg per week, achieved through a calorie deficit of 500-1,000 kcal/day. Faster loss risks muscle loss, nutritional deficiencies, and gallstones. For overweight individuals, even a 5-10% reduction in current weight (not necessarily reaching the "ideal") produces meaningful health benefits — improved blood pressure, blood sugar, and lipid profiles. The healthiest achievable weight is often more important than the theoretically ideal one.
Does weight matter more than fitness for health?
Research increasingly shows that cardiorespiratory fitness is a stronger predictor of mortality than weight. "Fat but fit" individuals — those who are overweight but have good aerobic fitness — have lower mortality than "thin but unfit" individuals. A study of 1.3 million people found fitness level was a stronger predictor of cardiovascular death than BMI across all weight categories. This suggests that for long-term health, activity and fitness may matter more than achieving a specific weight on the scale.
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.