Ideal Weight Calculator

How Ideal Weight Is Calculated

“Ideal weight” is a simplified clinical tool used to estimate medication dosing, anesthesia requirements, and nutritional targets. It is not a judgment about how you look, and it is not a goal weight. Several formulas exist, each developed by different researchers.

This page gives you two different answers because the question has two different meanings, and mixing them up is the mistake almost every ideal-weight page makes. The clinical ideal body weight is a single number per height, used for drug dosing. The healthy weight range from body mass index is a span of roughly 20 kg at the same height, and that is the one a person asking “what should I weigh” actually wants.

Devine formula (most clinically used):

For males:

IBW (kg) = 50 + 2.3 × (Height in inches − 60)

For females:

IBW (kg) = 45.5 + 2.3 × (Height in inches − 60)

Worked example, 5'9" male (69 inches):

IBW = 50 + 2.3 × (69 − 60) = 50 + 2.3 × 9 = 50 + 20.7 = 70.7 kg (156 lb)

Robinson formula (1983, slightly more accurate):

Males: IBW = 52 + 1.9 × (inches over 5 feet) Females: IBW = 49 + 1.7 × (inches over 5 feet)

Miller formula (1983):

Males: IBW = 56.2 + 1.41 × (inches over 5 feet) Females: IBW = 53.1 + 1.36 × (inches over 5 feet)

BMI-based ideal weight range:

Ideal weight range = BMI range (18.5–24.9) × Height (m)²

For someone 5'9" (1.753 m):

Low: 18.5 × 1.753² = 56.8 kg (125 lb) High: 24.9 × 1.753² = 76.5 kg (169 lb)

Notice how much wider that is than the three clinical formulas, which for the same 5'9" man land between 68.9 and 70.7 kg. A 5'9" man at 74 kg is a good 3 kg above every clinical ideal weight and still sits comfortably inside the healthy BMI range, at 24.1. Both statements are true at once, which is exactly why quoting only the first one is misleading.

Important context:

These formulas were developed for average-framed, Caucasian adults. They are less accurate for:

• Athletes, who come out looking underweight because muscle is denser than fat
• Anyone under 5 feet tall, where every one of these formulas breaks down completely
• Older adults, since bone density loss shifts the range

The height problem is worth spelling out, because most calculators quietly hide it. All three formulas start from a fixed weight at 60 inches and add per inch above that. Below 5 feet they run backwards: Devine gives a 4'4" woman 27 kg. Some sites clamp the answer at the 5-foot value, which is just as wrong in the other direction. This calculator refuses to print a clinical ideal weight below 60 inches and gives you the body mass index range instead, which works at any height.

Clinicians use ideal body weight mainly for drug dosing, chemotherapy and antibiotics in particular. It was never meant as a weight-loss target and does not work well as one.