Ideal weight calculator

What is an ideal weight calculator?

An ideal weight calculator estimates a healthy target body weight based on a person’s height and sex. Instead of relying on a single number, it reports four widely used clinical estimates side by side: the Devine, Robinson, Miller, and Hamwi formulas. Because each formula was derived from a different population and purpose, comparing them gives you a sensible range rather than one rigid figure.

Ideal body weight (IBW) is a reference value, not a strict goal. It is most often used in medicine to scale drug dosages and ventilator settings, and in fitness as a rough benchmark. Your healthy weight also depends on muscle mass, frame size, age, and overall health, so treat the result as a starting point for a conversation, not a verdict.

How does the calculator work?

You choose your sex and enter your height. All four formulas share the same structure: they start from a base weight at a height of 5 feet (60 inches) and add a fixed amount of weight for every inch above that. Heights are converted to inches internally, so you can enter centimeters, meters, inches, or feet and the calculator handles the conversion.

When a height is at or below 5 feet, the “inches over 60” term is zero, so the result equals the base weight of each formula. The calculator then displays the four estimates in kilograms.

Formulas

Let $h$ be height in inches and define the height above 5 feet as $\Delta = \max(h - 60, 0)$.

Devine (1974): $\text{IBW}_{\text{men}} = 50 + 2.3 \times \Delta$ $\text{IBW}_{\text{women}} = 45.5 + 2.3 \times \Delta$

Robinson (1983): $\text{IBW}_{\text{men}} = 52 + 1.9 \times \Delta$ $\text{IBW}_{\text{women}} = 49 + 1.7 \times \Delta$

Miller (1983): $\text{IBW}_{\text{men}} = 56.2 + 1.41 \times \Delta$ $\text{IBW}_{\text{women}} = 53.1 + 1.36 \times \Delta$

Hamwi (1964): $\text{IBW}_{\text{men}} = 48 + 2.7 \times \Delta$ $\text{IBW}_{\text{women}} = 45.5 + 2.2 \times \Delta$

All four return a weight in kilograms.

Examples

1. Man, 180 cm tall (≈ 70.87 in, so $\Delta \approx 10.87$ in):

   • Devine = $50 + 2.3 \times 10.87 \approx 75.0\ \text{kg}$
   • Robinson = $52 + 1.9 \times 10.87 \approx 72.6\ \text{kg}$
   • Miller = $56.2 + 1.41 \times 10.87 \approx 71.5\ \text{kg}$
   • Hamwi = $48 + 2.7 \times 10.87 \approx 77.3\ \text{kg}$

2. Woman, 165 cm tall (≈ 64.96 in, so $\Delta \approx 4.96$ in):

   • Devine = $45.5 + 2.3 \times 4.96 \approx 56.9\ \text{kg}$
   • Robinson = $49 + 1.7 \times 4.96 \approx 57.4\ \text{kg}$
   • Miller = $53.1 + 1.36 \times 4.96 \approx 59.8\ \text{kg}$
   • Hamwi = $45.5 + 2.2 \times 4.96 \approx 56.4\ \text{kg}$

Which formula should you use?

• Devine is the most common in clinical pharmacy and is the default for many drug-dosing references.
• Robinson and Miller were published as refinements of Devine and tend to give slightly lower estimates.
• Hamwi is a quick bedside rule that often produces the highest male estimate.

Because the formulas disagree by a few kilograms, the spread between them is itself useful information: it shows how much “ideal weight” depends on the method rather than on objective biology.

Practical notes

• These formulas use only height and sex. They do not account for frame size, body composition, or athletic muscle mass, so very muscular people may exceed their “ideal” weight while remaining lean.
• Ideal body weight is not the same as a healthy weight range. For a height-and-weight based screening of weight status, use the BMI calculator.
• To estimate how much of your weight is fat versus lean tissue, see the body fat calculator.

FAQs

Is ideal body weight the same as a healthy weight?

No. Ideal body weight is a single reference figure derived from height and sex, while a healthy weight is a range that also depends on body composition, age, and frame. Use IBW as a benchmark, not a strict target.

Why does the calculator show four different numbers?

Each formula was created by a different author for a slightly different purpose, so they give slightly different estimates. Showing all four lets you see a realistic range instead of a single rigid value.

Does the calculator account for muscle mass?

No. The formulas use only height and sex. Athletes and very muscular people may weigh more than their calculated ideal weight while still being healthy, which is why body composition tools are a useful complement.

What if I am shorter than 5 feet?

For heights of 5 feet or less, the “inches over 60” term is zero, so each formula simply returns its base weight. These formulas were designed for adults and are least reliable at very short heights.