Ideal Weight Calculator: Hamwi, Devine, Robinson & Miller Formulas Explained

Finding your ideal body weight is one of the most common health questions — and one of the most misunderstood. There is no single "correct" ideal weight. Different medical formulas give different answers, and that's by design: each was developed for a specific clinical purpose. Our ideal weight calculator uses all four major formulas simultaneously so you can see the full picture.

What is Ideal Body Weight?

Ideal body weight (IBW) is a target weight range associated with good health outcomes and lower risk of weight-related disease. It is not a cosmetic standard — it is a clinical tool used by doctors and pharmacists to calculate drug dosages, assess nutritional status, and set realistic weight-management goals.

Unlike BMI alone, IBW formulas account for gender (because men and women carry weight differently) and can be adjusted for frame size (small, medium, or large bone structure).

The 4 Ideal Weight Formulas

Hamwi Formula (1964)

The Hamwi formula is the most widely used in clinical practice, especially in the United States:

• Male: 48.0 kg + 2.7 kg per inch over 5 feet
• Female: 45.5 kg + 2.2 kg per inch over 5 feet

Developed by Dr. G.J. Hamwi, it was originally designed for calculating insulin requirements and remains popular in hospital settings.

Devine Formula (1974)

The Devine formula was originally developed to calculate drug dosages, particularly for medications where body weight affects dosing:

• Male: 50.0 kg + 2.3 kg per inch over 5 feet
• Female: 45.5 kg + 2.3 kg per inch over 5 feet

It is widely used in pharmacokinetics and anaesthesia to determine ideal weight for medication dosing.

Robinson Formula (1983)

Robinson et al. published a modification of the Devine formula based on statistical analysis of population data:

• Male: 52.0 kg + 1.9 kg per inch over 5 feet
• Female: 49.0 kg + 1.7 kg per inch over 5 feet

The Robinson formula tends to give slightly lower estimates than Hamwi, especially at taller heights.

Miller Formula (1983)

The Miller formula was also published in 1983 and generally gives higher estimates than the other three:

• Male: 56.2 kg + 1.41 kg per inch over 5 feet
• Female: 53.1 kg + 1.36 kg per inch over 5 feet

Because it produces higher values, some consider it better suited for larger-framed individuals.

BMI-Based Ideal Weight Range

In addition to the four formulas, our calculator shows the healthy BMI weight range for your height:

• Minimum healthy weight: BMI = 18.5 × height² (in meters)
• Maximum healthy weight: BMI = 24.9 × height² (in meters)

This gives you a range rather than a single number, which many health professionals consider more realistic.

Frame Size Adjustment: Why It Matters

Two people of the same height and gender can have very different healthy weights depending on their bone structure. Our calculator applies a ±10% adjustment:

Frame Size	Adjustment	Who It Applies To
Small	−10%	Narrow wrists, light bone structure
Medium	0%	Average bone structure
Large	+10%	Wide wrists, heavy bone structure

A simple way to estimate frame size: wrap your thumb and middle finger around your wrist. If they overlap, you have a small frame; if they just touch, medium; if they don't meet, large.

How to Use This Calculator

1. Select your unit system (metric or imperial)
2. Enter your height
3. Choose your gender
4. Select your frame size (small / medium / large)
5. Review the results from all four formulas, the BMI range, and your frame-adjusted ideal weight

Which Formula Should You Use?

There is no single "best" formula — they were designed for different purposes:

• Clinical/medical use: Hamwi or Devine are standard
• Drug dosing: Devine is most common
• General wellness goal setting: Use the average of all four formulas, or the BMI range
• Larger-framed individuals: Miller tends to give more appropriate estimates

The average of the four formulas shown in our calculator provides a balanced estimate suitable for most people.

Ideal Weight vs. Healthy Weight: What's the Difference?

"Ideal weight" and "healthy weight" are often used interchangeably, but they have subtle differences:

• Ideal weight from formulas is a single target number based on height and gender
• Healthy weight (BMI range) is a range based on population health outcomes
• Personal optimal weight takes into account muscle mass, bone density, age, fitness level, and individual health history

Most health professionals recommend aiming for a weight within the healthy BMI range rather than chasing a single formula number.

Frequently Asked Questions

How accurate are ideal weight formulas?

These formulas are population-level estimates developed from studies conducted decades ago. They are reasonably accurate for average-framed adults but can underestimate ideal weight for very muscular individuals and overestimate for elderly populations with reduced muscle mass. Use them as a starting point, not a precise target.

Why do the formulas give different results?

Each formula was derived from a different dataset and developed for a different clinical purpose. Hamwi (1964) was designed for diabetes management, Devine (1974) for pharmacokinetics, Robinson and Miller (both 1983) for general weight estimation. The differences between formulas are usually within 5–10%, which is why taking the average is recommended for general wellness purposes.

What should I do if I'm above my ideal weight?

Being above the formula-based ideal weight does not necessarily mean you are unhealthy. If your BMI is in the healthy range (18.5–24.9) and you have no weight-related health conditions, your weight may already be fine for your body. If you have concerns, consult a doctor or registered dietitian rather than targeting a specific formula number.

Does ideal weight change with age?

The standard formulas do not account for age, but research suggests that slightly higher BMI values (around 25–27) may be associated with better health outcomes in adults over 65. Older adults tend to lose muscle mass, so the formulas may not be the most appropriate targets for elderly populations.

How does frame size affect ideal weight?

Frame size reflects bone density and skeletal structure. A person with a large frame (heavier bones, wider skeleton) will naturally weigh more than a small-framed person of the same height at the same level of health. The ±10% frame adjustment in this calculator is a widely accepted clinical guideline.

Can I use this calculator for children?

No — these formulas are validated for adults only. Children's ideal weight is determined using age-and-sex-specific growth charts (percentiles), not adult IBW formulas.

Is ideal weight the same as goal weight for weight loss?

Not necessarily. Your goal weight should be determined based on your current health status, medical history, fitness level, and lifestyle — ideally in consultation with a healthcare professional. The ideal weight formulas give a useful reference point, but a sustainable, achievable goal weight may differ.

Tips for Achieving Your Ideal Weight

• Focus on gradual, sustainable changes (0.5–1 kg per week maximum)
• Combine balanced nutrition with regular physical activity
• Track progress using multiple metrics: weight, waist circumference, energy levels, and fitness performance
• Use our BMI Calculator and TDEE Calculator alongside ideal weight for a complete picture
• Consult a registered dietitian for a personalised plan