What is my ideal weight?

The concept of "ideal body weight" has been both useful and controversial in medicine and nutrition for over a century. Unlike BMI, which provides a statistical indicator of weight relative to height, ideal weight formulas attempt to calculate a specific target weight for an individual based on their height and sex. These formulas are routinely used in clinical medicine — particularly for calculating drug dosages (many medications are dosed based on ideal body weight rather than actual weight), assessing nutritional status, and providing patients with a concrete and personalized weight goal in obesity management programs.

Several ideal weight formulas have been developed over the decades, each derived from different population datasets and with slightly different mathematical approaches. The two most commonly used in modern clinical practice are the Devine formula (1974), originally derived for pharmacokinetic dosing studies, and the Robinson formula (1983), which provides slightly higher values and is often cited in sports medicine and fitness contexts. Understanding what these formulas measure — and what their limitations are — helps you use them as a useful guide rather than a rigid prescription.

How does the ideal weight calculation work?

Both formulas use the same two inputs:

• Height: in feet and inches (US) or centimeters (metric). The formulas use height above 5 feet (60 inches / 152.4 cm) as their baseline.
• Sex: male or female. The formulas differ by sex to account for structural differences in bone density, frame size, and typical body composition.

Devine formula (1974):

Men: IBW (kg) = 50 + 2.3 × (height in inches – 60)

Women: IBW (kg) = 45.5 + 2.3 × (height in inches – 60)

Robinson formula (1983):

Men: IBW (kg) = 52 + 1.9 × (height in inches – 60)

Women: IBW (kg) = 49 + 1.7 × (height in inches – 60)

Metric conversion tip: To convert height in centimeters to inches, divide by 2.54. For example, 178 cm ÷ 2.54 = 70.1 inches ≈ 5'10".

Both formulas assume a medium body frame. Individuals with large frames may comfortably exceed the predicted value; those with small frames may be healthy at slightly below it. A useful range is the predicted value ±10% to account for individual variation.

Concrete example

Let's calculate the ideal weight for a 5'10" (70 inches) male. Height above 60 inches: 70 – 60 = 10 inches.

Devine formula: IBW = 50 + 2.3 × 10 = 50 + 23 = 73 kg (160.6 lbs).

Robinson formula: IBW = 52 + 1.9 × 10 = 52 + 19 = 71 kg (156.5 lbs).

The two formulas give similar results — 71 to 73 kg — suggesting that for a 5'10" man, a healthy reference weight is approximately 71–73 kg. Applying a ±10% range: 64–80 kg. This corresponds to a BMI range of roughly 19.9 to 25.0 — solidly within or just touching the upper boundary of normal weight, consistent with the WHO classification.

Now let's look at a 5'5" (65 inches) woman. Height above 60 inches: 65 – 60 = 5 inches. Devine: 45.5 + 2.3 × 5 = 45.5 + 11.5 = 57 kg (125.7 lbs). Robinson: 49 + 1.7 × 5 = 49 + 8.5 = 57.5 kg (126.8 lbs). In this case, both formulas converge almost perfectly on 57 to 57.5 kg, providing a very clear reference point for a woman of this height. Applying the ±10% range: 51.3 to 63.3 kg — a generous window that accommodates different body types.

It is worth emphasizing that these calculations should be treated as reference ranges, not personal mandates. A highly muscular woman who weighs 65 kg at 5'5" with low body fat may be in excellent health despite being above the Devine ideal weight. The goal of ideal weight formulas is to give a useful clinical anchor, not to define your worth or set an unrealistic aesthetic standard.

Frequently asked questions