Ideal Weight Calculator

What Is Ideal Body Weight?

Ideal body weight (IBW) is the weight at which a person of a given height and sex is considered to be at their healthiest. It is not a single magic number but rather a scientifically-derived estimate used in clinical medicine for purposes including medication dosing, mechanical ventilation settings, nutritional prescriptions, and surgical risk assessment.

The term was first used systematically in actuarial science — life insurance companies in the early 20th century identified the weights at which mortality risk was lowest for given height categories. This work later inspired the development of the BMI scale and the specific IBW formulas used in medicine today.

For most people, the most practical definition of ideal weight is simply the healthy weight range for your height — corresponding to a BMI of 18.5–24.9 as defined by the NHS and WHO. This range acknowledges that there is no single "perfect" weight and that a band of weights is compatible with good health at any height.

The four formulas used in our calculator — Devine, Hamwi, Robinson and Miller — were all developed between 1964 and 1983 and remain widely referenced in clinical and nutritional medicine. They produce slightly different estimates, particularly at heights significantly above or below the average, which is why taking the average of all four provides the most balanced estimate.

Is Ideal Weight the Right Goal?

Ideal body weight formulas were originally designed for clinical use — particularly for calculating medication doses based on lean body mass, which correlates better with drug clearance than total body weight. For this reason, they should not be treated as the sole target for personal weight management.

For most people, a more meaningful and flexible target is reaching the healthy BMI range of 18.5–24.9. This allows for individual variation in body composition, muscularity, and frame size. A heavily-muscled man who weighs above the Devine IBW but has low body fat and excellent metabolic health is clearly not "overweight" in any clinically meaningful sense.

Limitations of IBW Formulas

• They don't account for body composition. Muscle weighs more than fat — a lean, muscular person may exceed their IBW without any health risk.
• They weren't designed for very tall or very short people. The formulas were derived from populations of average height and become less accurate at extremes.
• They don't account for age. Some evidence suggests slightly higher weights are optimal in older adults, where low body weight is associated with worse outcomes.
• They don't account for ethnicity. Some populations (particularly South and East Asian) have higher metabolic risk at lower BMIs and may benefit from lower ideal weight targets.

The most comprehensive health assessment combines BMI, waist circumference, body fat percentage, blood pressure, fasting glucose and lipid profile — not a single number from any formula. Use the ideal weight calculator above as a practical starting point, not a definitive clinical verdict.

How to Reach Your Ideal Weight

Whether you need to lose weight, gain weight, or maintain your current weight, the principles are the same: manage energy balance through diet and physical activity, preserve or build lean muscle mass, and adopt sustainable habits that can be maintained long-term.

If You Need to Lose Weight

A moderate calorie deficit of 500–750 kcal/day produces approximately 0.5–0.75 kg of weight loss per week — the rate recommended by the NHS for sustainable fat loss. Prioritise protein (1.6–2.2 g/kg bodyweight) to preserve lean mass during deficit. Resistance training alongside a calorie deficit produces superior body composition outcomes compared to cardio alone.

If You Need to Gain Weight

A moderate calorie surplus of 300–500 kcal/day combined with progressive resistance training promotes lean mass gain with minimal fat accumulation. Focus on protein-rich whole foods, complex carbohydrates, and healthy fats. Gaining weight too rapidly (more than 0.5 kg/week) tends to accumulate more fat than muscle.

If You're Already at a Healthy Weight

Focus on maintaining weight through balanced eating and regular activity. The NHS recommends at least 150 minutes of moderate-intensity activity per week. Monitoring weight weekly and adjusting intake if you drift more than 2–3 kg from your healthy range is a practical and evidence-based strategy.