Ideal Weight: 4 Formulas, 4 Different Numbers — Here's What Each One Actually Means
Ideal Weight: 4 Formulas, 4 Different Numbers — Here's What Each One Actually Means
You step on the scale. The number stares back. You search "ideal weight for my height" and get four different answers from four different calculators. Now what?
This is the problem with the concept of "ideal weight." It sounds like there should be one correct number, like a target on a dartboard. But the reality is messier — and more useful — than that. The four major formulas used by doctors and researchers were developed decades apart, for different populations, with different goals in mind. They give different results because they're answering slightly different questions.
Let me walk through each one, where it came from, and what it actually tells you.
The Four Formulas — And Where They Came From
Devine Formula (1974)
Developed for one very specific purpose: calculating drug dosages. Dr. Devine wasn't trying to define a healthy weight. He needed a standard way to compute medication doses based on body size, and he needed it to be simple enough to use at a bedside. For men, the formula starts at 50 kg for 5 feet and adds 2.3 kg per inch over that. For women, it starts at 45.5 kg. It was never intended as a health benchmark, yet it became the most commonly used formula in clinical settings for decades.
Robinson Formula (1983)
Based on data from the 1959 Metropolitan Life Insurance tables — yes, life insurance data from the 1950s. These tables represented the weights associated with the lowest mortality rates among insured Americans at the time. The Robinson formula adjusts Devine's numbers downward slightly, because the insurance data suggested that the weights associated with longest life were a bit lower than what Devine's drug-dosing formula produced.
Miller Formula (1983)
Published the same year as Robinson, but based on more recent military and civilian data. Miller's formula produces a higher ideal weight for most people, particularly taller individuals. The rationale: more recent generations were both taller and heavier, and that didn't seem to be making them less healthy. Miller's formula reflects a more modern understanding of weight ranges.
Hamwi Formula (1964)
The oldest of the four, and the simplest. Dr. Hamwi was a physician who wanted a quick mental calculation for determining ideal weight in a clinical setting without needing charts or calculators. It's the most generous formula for shorter people and the most restrictive for taller people. It's also the least validated by research, but it remains popular because it's easy to remember: 106 pounds for 5 feet of height, plus 6 pounds per inch for men (100 pounds for women, plus 5 pounds per inch).
Why These Numbers Are Different
Take a 5-foot-10-inch man and run him through all four formulas:
- Devine: 73 kg (161 lbs)
- Robinson: 69 kg (152 lbs)
- Miller: 75 kg (165 lbs)
- Hamwi: 71 kg (157 lbs)
That's a 6 kg spread — about 13 pounds. Which one is "right"? None of them, and all of them. The formulas were developed for different purposes and different populations. The Devine formula was for drug dosing (so it's conservative). The Robinson formula was based on life insurance data (so it reflects the lowest-risk population from the 1950s). The Miller formula was based on broader population data (so it's more forgiving). The Hamwi formula was a clinical shortcut (so it's a general guideline, not a research-backed standard).
Using our Ideal Weight Calculator, you can see all four results side by side and get a range rather than a single number. That range is more useful than any individual formula because it acknowledges the uncertainty in the concept itself.
🔗 Bookmark the tool: Use our free Ideal Weight Calculator to check your ranges.
The Bigger Problem With "Ideal Weight"
Here's something most calculator websites won't tell you: the entire concept of "ideal weight" based on height alone is fundamentally limited. It doesn't account for muscle mass, bone density, body composition, or where you carry your fat. A 180-pound powerlifter at 12% body fat and a 180-pound sedentary person at 30% body fat have the same "ideal weight" by these formulas. They are not equally healthy.
This is where the BMI range actually helps. BMI at least gives you a range (18.5 to 24.9) rather than a single number, which acknowledges that healthy weight falls on a spectrum. But BMI has its own well-documented flaws — it systematically misclassifies muscular people as "overweight" and can miss unhealthy fat distribution in people who fall in the "normal" range by BMI.
The most useful approach is to use the ideal weight formulas and BMI range as starting points, then cross-reference with actual body composition metrics:
- Body fat percentage: A better indicator of metabolic health than weight alone
- Waist circumference: Excess abdominal fat is particularly risky, regardless of overall weight
- How you feel: Energy levels, sleep quality, and how your clothes fit are also valid metrics
When Ideal Weight Formulas Are Actually Useful
Despite their limitations, these formulas are still used for a reason. They're helpful in specific situations:
- Medical dosing: The Devine formula is still standard for calculating certain medication doses
- Screening tools: Doctors use them as quick reference points during checkups
- Goal setting: If you're significantly overweight, any of these formulas can give you a first target to work toward
The problem isn't the formulas themselves. It's treating any single number as a verdict instead of a data point. Your body doesn't know about Devine or Robinson or Hamwi. It responds to what you eat, how you move, how you sleep, and how you manage stress. Use the calculator, take the range it gives you, and then assess based on the full picture — not just a number on a scale.
The Bottom Line
The four ideal weight formulas give different answers because they're asking different questions. None of them is "the truth" about what you should weigh. The best approach is to use them as context, look at the full range they produce, and check that range against other health indicators like body fat percentage and waist circumference.
Weight is a data point, not a identity. Treat it like one.
Disclaimer: The ideal weight formulas presented are general guidelines based on population data. Individual factors such as muscle mass, bone density, and overall body composition affect what a healthy weight means for you. Consult a healthcare provider for personalized medical advice.