Ideal Weight Calculator
Ideal body weight (IBW) is a clinical estimate of the weight associated with the lowest health risk for a given height and sex. Multiple formulas exist, this calculator uses the most established: the Devine formula (used in hospital pharmacology for drug dosing), the Robinson formula (a refinement of Devine), and the BMI method (targeting BMI 18.5–24.9). Each produces slightly different results because they were derived from different study populations. Importantly, IBW is a clinical benchmark, not a body image target, a muscular athlete or older adult may have a healthy body composition at weights outside the standard IBW range. In Australia, the Therapeutic Goods Administration and hospital pharmacists use IBW-based formulas for medication dosing and nutritional support calculations. Athletes should note that muscle weighs more than fat, so IBW estimates may understate healthy weight for high lean-muscle individuals. Results are shown across all three formulas.
Frequently Asked Questions
What is ideal body weight?
Ideal body weight (IBW) is an estimate of a healthy weight range for your height, derived from population data and used as a clinical reference. The classic Devine formula (developed for medical drug dosing) calculates: 50 + 2.3 kg per inch over 5 feet for men, and 45.5 + 2.3 kg per inch over 5 feet for women. More modern approaches use BMI ranges (18.5-24.9) which give a broader, healthier range. IBW formulas are rough guidelines - they don't account for muscle mass, bone density, sex, or ethnicity.
What is the BMI-based ideal weight range?
For most adults, a BMI of 18.5-24.9 is considered a healthy weight range. For someone 175cm tall, this corresponds to approximately 57-77 kg. For 180cm: 60-81 kg. For 165cm: 50-68 kg. This range captures the weight at which population-level health outcomes (cardiovascular disease, type 2 diabetes, mortality) are most favourable. The BMI-based range is more reliable than older IBW formulas because it's grounded in actual health outcome data rather than actuarial assumptions.
Is the "ideal weight" the same as "target weight"?
No. Ideal weight is a population estimate based on height and sex - a general reference point. Target weight is personal and individualised, accounting for your body composition goals, health markers, activity level, and how you actually feel at a given weight. Your target weight might be above or below your IBW depending on whether you're building muscle (which weighs more than fat) or prioritising leanness for performance.
Does muscle weigh more than fat?
Muscle is denser than fat, meaning it takes up less space per kilogram. A muscular person may weigh more but wear a smaller clothing size than someone with the same weight but a higher body fat percentage. This is why the scale alone can be misleading - tracking body composition changes over time is more useful than chasing a specific weight. For a simple, affordable way to track body composition changes, the MyoTape body measuring tape lets you measure waist, arms, chest, and thighs with one button-press release. Consistent measurements every few weeks reveal whether you're gaining muscle or losing fat even when the scale isn't moving.
What are the health risks of being underweight?
Being underweight (BMI under 18.5) can weaken the immune system, reducing your ability to fight off infections. It can also reduce bone density, increasing the risk of osteoporosis and fractures. In women, low body weight can affect hormone production and fertility. Other risks include anemia (from inadequate iron intake), muscle wasting, fatigue, and in severe cases, heart irregularities. If you're struggling to maintain a healthy weight, consult a doctor or dietitian.
How should I set my own weight goal?
Focus on health outcomes and how you feel, not just a number on the scale. Strength, energy levels, blood pressure, cholesterol, and sleep quality matter more than hitting a specific weight. Consider body composition goals (like reducing body fat percentage) or performance goals (like running 5km in under 25 minutes) rather than chasing an arbitrary number. Burn the Fat, Feed the Muscle by Tom Venuto is a comprehensive guide to body transformation that covers nutrition, resistance training, and mindset, helping you set realistic, sustainable goals.