Many people want a single number that says what they should weigh. Several formulas offer one, but they give different answers, and none of them can see your muscle mass, age or body shape. This guide compares the most common ideal weight formulas, shows how to use them, and explains why a healthy range is a better goal than a target number.

The Four Classic Formulas

The best-known formulas use height only. They were developed decades ago, in several cases for estimating medication doses, not for judging health. Each adds a base weight for 5 feet (60 inches) of height plus a set amount for every inch above that.

  • Devine (1974): men 50 kg + 2.3 kg per inch over 5 feet; 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.
  • Hamwi (1964): men 48 kg + 2.7 kg per inch; women 45.4 kg + 2.3 kg per inch.

A Worked Example for a Height of 170 cm

A height of 170 cm is 66.93 inches, which is 6.93 inches over 5 feet. The formulas give:

  • Devine: 65.9 kg for men, 61.4 kg for women.
  • Robinson: 65.2 kg for men, 60.8 kg for women.
  • Miller: 66.0 kg for men, 62.5 kg for women.
  • Hamwi: 66.7 kg for men, 61.1 kg for women.

Notice that the results cluster within a few kilograms of each other, which is typical. The real lesson is that precision is an illusion: any single number is just a rough guide.

The BMI Healthy Range

The World Health Organization defines a healthy BMI as 18.5 to 24.9. At 1.70 m, that corresponds to weights from 18.5 × 1.70² = 53.5 kg to 24.9 × 1.70² = 72.0 kg. This is a wide range of about 18 kg, and it is a more realistic way to think about healthy weight than any single formula. For people of Asian descent, health risks can rise at lower BMI levels, so the range may need to be narrower; see our guide to BMI and Asian populations.

What These Formulas Miss

  • Body composition: a muscular person can weigh more than the formula suggests and be perfectly healthy. Our article on BMI versus body fat covers this.
  • Age: healthy weight tends to creep up in older age, and carrying slightly more weight is sometimes protective after 65.
  • Frame size and bone structure: two people of the same height can differ in frame by several kilograms.
  • Fat distribution: fat around the waist carries more health risk than fat on the hips and thighs.
  • Sex, pregnancy and medical conditions, which formulas ignore completely.

Better Indicators to Add

  • Waist circumference: risk increases above about 94 cm for men and 80 cm for women in European populations, and at lower thresholds for some Asian groups.
  • Waist-to-height ratio: keeping your waist below half your height is a simple target.
  • Blood pressure, blood sugar and cholesterol from a routine health check.
  • How you feel: energy, sleep, strength and fitness.

How to Use a Weight Target Wisely

  • Treat the result as a range of about plus or minus 10%, not a goal to hit exactly.
  • Set small goals, such as losing 0.25 to 0.5 kg a week, rather than aiming for a number on the scale.
  • Focus on habits: regular movement, adequate protein, whole foods and enough sleep. Our calorie guide explains how to estimate your daily needs.
  • If you are underweight, have a history of disordered eating, are pregnant or have a medical condition, talk to a healthcare professional before setting any target.

Use a range

Take the BMI range for your height as the outer boundary, check your waist against the thresholds, and treat the formulas as a sanity check. If you are outside the range, talk to a clinician before setting a target.