What Is Ideal Body Weight?

Ideal body weight (IBW) is a clinical estimate of how much a person should weigh based primarily on their height and gender. The concept was originally developed in the 1960s and 1970s to help physicians calculate correct medication dosages, especially for drugs where dosing by actual body weight could be dangerous for obese or underweight patients.

Over the decades, IBW has become a widely used benchmark in nutrition planning, fitness programmes, insurance assessments, and general health screening. However, it is essential to understand that IBW is a simplified estimate. It does not factor in muscle mass, bone density, age, ethnicity, or individual body composition.

Think of ideal body weight as a starting point for conversation with your doctor — not as a definitive verdict on your health.

The Four Major Ideal Weight Formulas

Several medical researchers have developed formulas to estimate ideal body weight. Each uses height in inches (specifically, inches above 5 feet or 60 inches) as the primary variable. Here are the four most widely referenced formulas used in clinical and wellness settings.

Devine Formula (1974)

The Devine formula is the most commonly cited IBW formula worldwide. Dr. B.J. Devine originally introduced it for calculating drug dosages, particularly gentamicin. For males, the formula starts at 50 kg for a height of 5 feet, adding 2.3 kg for each additional inch. For females, it starts at 45.5 kg.

Robinson Formula (1983)

Robinson and colleagues refined Devine's approach using updated population data. The male formula begins at 52 kg with a per-inch increment of 1.9 kg, while females start at 49 kg with 1.7 kg per inch. Robinson's formula tends to produce slightly lower estimates for taller individuals.

Miller Formula (1983)

The Miller formula uses higher base weights (56.2 kg for males, 53.1 kg for females) but smaller per-inch increments (1.41 kg and 1.36 kg respectively). This results in a narrower range of variation across different heights and generally yields higher estimates for shorter individuals.

Hamwi Formula (1964)

Dr. G.J. Hamwi's formula is the oldest of the four and is still used in many dietetics programmes. It uses a male base of 48 kg with a 2.7 kg per-inch increment — the highest increment of all four formulas — making it produce the highest estimates for very tall individuals.

How Body Frame Size Affects Ideal Weight

Body frame size is an important modifier to ideal weight calculations. People with larger skeletal frames naturally carry more bone and connective tissue mass, which should be reflected in their weight targets.

Frame size is typically categorised as small, medium, or large. A common method to estimate frame size is by measuring wrist circumference and comparing it to height-based reference charts.

• Small frame: Reduces the ideal weight estimate by approximately 10%.
• Medium frame: Uses the standard formula result without adjustment.
• Large frame: Increases the ideal weight estimate by approximately 10%.

For instance, a male at 5'10" might have a Devine IBW of 73.0 kg with a medium frame, but 65.7 kg with a small frame and 80.3 kg with a large frame.

Ideal Weight vs. BMI: Understanding the Difference

Many people confuse ideal body weight with Body Mass Index (BMI), but they are distinct concepts. IBW uses height-based linear formulas to produce a single target weight. BMI, on the other hand, is a ratio calculated as weight divided by height squared (kg/m²).

A healthy BMI falls between 18.5 and 24.9. Using this range, you can calculate a healthy weight range for any height. For example, someone who is 170 cm tall would have a healthy BMI weight range of approximately 53.5 kg to 72.0 kg.

Our Ideal Weight Calculator shows both IBW results and the BMI-based healthy weight range, giving you a more complete picture.

Real-World Examples of Ideal Weight Calculations

Limitations of Ideal Weight Formulas

While ideal weight formulas are useful reference points, they come with significant limitations that you should be aware of before using them to guide health decisions.

• No muscle mass consideration: A muscular athlete may weigh far more than their IBW and still be extremely healthy. These formulas cannot distinguish between muscle and fat.
• Age not factored: Body composition changes with age. A 25-year-old and a 65-year-old at the same height will likely have different healthy weight ranges, but IBW formulas treat them identically.
• Ethnic diversity ignored: These formulas were primarily developed using Western population data. Body proportions and healthy weight ranges can differ significantly across ethnicities.
• Below 5 feet limitation: All four formulas use inches above 60 (5 feet) as their variable. For individuals shorter than 5 feet, the formulas yield only the base value, which may not be accurate.
• Outdated data: The most recent formula (Robinson) is from 1983. Population health profiles have changed considerably since then.

For a more comprehensive health assessment, consider using IBW alongside BMI, body fat percentage, waist-to-hip ratio, and advice from a qualified healthcare professional.

How to Determine Your Body Frame Size

Knowing your body frame size helps you get more accurate ideal weight estimates. The simplest method uses wrist circumference. Wrap a tape measure around your wrist at the narrowest point just below the wrist bone and compare against these reference charts.

For Males

• Height over 5'5": Small frame < 6.75", Medium 6.75"–7.5", Large > 7.5"
• Height 5'2"–5'5": Small frame < 6.5", Medium 6.5"–7.0", Large > 7.0"

For Females

• Height over 5'2": Small frame < 6.25", Medium 6.25"–6.5", Large > 6.5"
• Height under 5'2": Small frame < 5.5", Medium 5.5"–5.75", Large > 5.75"

If you do not have a tape measure, another quick estimate is to wrap your thumb and middle finger around your wrist. If the fingers overlap, you likely have a small frame. If they just touch, medium. If they do not meet, you have a large frame.

When Should You Consult a Doctor?

Ideal weight calculators are informational tools, not diagnostic instruments. You should consult a healthcare professional if any of the following apply to you.

• Your current weight is significantly above or below the calculated ideal range.
• You are planning major dietary changes or starting a new exercise programme.
• You have a medical condition that affects weight, such as thyroid disorders, diabetes, or PCOS.
• You are pregnant, breastfeeding, or recovering from an illness.
• You feel confused about conflicting information from different weight metrics.

A doctor can evaluate your complete health picture — including blood work, body composition analysis, and lifestyle factors — to provide guidance that no online calculator can match.

Tips for Reaching and Maintaining a Healthy Weight

Once you know your ideal weight range, here are practical evidence-based strategies to work towards and maintain it.

• Focus on gradual changes: Aim for 0.5–1 kg of weight change per week. Rapid weight loss often leads to muscle loss and is difficult to sustain.
• Prioritise nutrition quality: Focus on whole grains, lean proteins, fruits, vegetables, and healthy fats rather than calorie counting alone.
• Stay physically active: The WHO recommends at least 150 minutes of moderate-intensity physical activity per week for adults.
• Get adequate sleep: Poor sleep disrupts hunger hormones (ghrelin and leptin) and can lead to weight gain over time.
• Manage stress: Chronic stress increases cortisol, which promotes fat storage, particularly around the abdomen.
• Track progress wisely: Use multiple metrics — weight, waist measurement, energy levels, and how your clothes fit — rather than relying on the scale alone.