Ideal weight formulas compared: Devine, Robinson, Miller and Hamwi

The classic ideal body weight formulas all work the same way: start with a fixed weight for a person 5 feet (152.4 cm) tall and add a set amount for every inch above that. They give similar answers for average heights and drift apart for very tall or short people. None of them was designed to tell an individual what they should weigh. The ideal weight calculator shows all four side by side with the healthy BMI range, and this guide explains where each comes from and how to read them.

The four formulas

Each formula gives a base weight in kilograms at 5 feet, plus a number of kilograms per inch over 5 feet:

• Hamwi (1964) — men 48 kg + 2.7 kg per inch; women 45.5 kg + 2.2 kg per inch. In pounds this is the familiar rule of thumb: about 106 lb plus 6 lb per inch for men, and 100 lb plus 5 lb per inch for women.
• Devine (1974) — men 50 kg + 2.3 kg per inch; women 45.5 kg + 2.3 kg per inch.
• Robinson (1983) — men 52 kg + 1.9 kg per inch; women 49 kg + 1.7 kg per inch.
• Miller (1983) — men 56.2 kg + 1.41 kg per inch; women 53.1 kg + 1.36 kg per inch.

The per-inch amount is what makes them diverge. Hamwi adds the most per inch, so it gives the highest figures for tall people; Miller adds the least but starts higher, so it gives higher figures for shorter people.

Where they came from

Hamwi's figures, published in 1964, became a widely used rule of thumb. Ben Devine published his formula in 1974 to estimate drug clearance and doses, particularly in patients with obesity, where dosing by total body weight can give the wrong answer for some medicines. Devine's version is still the most widely used in clinical settings, mainly for calculating doses and estimating kidney function. Robinson and Miller both published alternatives in 1983 with the same straight-line shape and different constants. The term ideal body weight itself grew out of insurance tables that linked height and weight to life expectancy, which reflected the people being insured rather than the whole population.

Worked examples

For a man 175 cm (5 ft 9 in) tall, about 8.9 inches over 5 feet, the calculator gives: Hamwi 72.0 kg, Devine 70.5 kg, Robinson 68.9 kg and Miller 68.7 kg. The four agree within about 3 kg, roughly 152 to 159 lb.

For a woman 165 cm (5 ft 5 in) tall, about 5 inches over 5 feet: Hamwi 56.4 kg, Devine 56.9 kg, Robinson 57.4 kg and Miller 59.8 kg, a spread of about 124 to 132 lb. Below 5 feet the formulas subtract weight for every inch under, and quickly become unreliable; the calculator warns about this and suggests the BMI range instead.

How they compare with BMI

The formulas give a single number; the BMI approach gives a range. A healthy BMI of 18.5 to 24.9 corresponds to about 56.7 to 76.3 kg for the 175 cm man, and about 50.4 to 67.8 kg for the 165 cm woman. All four formula results sit comfortably inside those ranges. That is a useful reminder that a wide band of weights is consistent with good health. The NHS notes that people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds face higher health risks at a lower BMI, with overweight starting at 23 rather than 25. The BMI calculator gives your own figure, and Is BMI accurate? explains its strengths and weaknesses.

What they leave out

Height and sex are the only inputs, so the formulas ignore muscle mass, frame size, age, body fat distribution and ethnicity. A muscular athlete may weigh well above every formula and be very healthy; someone at the formula weight may still carry a lot of fat around the waist. They were built for clinical and population use, not for setting personal goals, and chasing one exact number can be unhelpful or even harmful, particularly for anyone with a history of disordered eating.

Better measures to use alongside

For a fuller picture of whether your weight is a health concern, combine several measures:

• Waist-to-height ratio: the NHS suggests keeping your waist to less than half your height; the waist-to-height calculator checks it.
• Body fat estimates, such as the circumference method in the body fat calculator, covered in How body fat percentage is estimated — and how much to trust each method.
• Health markers such as blood pressure, blood sugar and cholesterol, plus fitness, energy and how you feel.

If you want to change your weight, the trend matters more than any single day; the weight tracker smooths out daily swings. A GP or registered dietitian can tell you what is a healthy weight for you, especially if you have a medical condition.