“Ideal weight” sounds like it should have one clean answer. It doesn’t. Several different formulas exist, each developed decades apart for different purposes, and they don’t always agree with each other. Here’s how the major ones work, a real worked example, and why the number they spit out deserves some healthy skepticism.
The Major Ideal Weight Formulas
Several formulas have been used in medicine and fitness over the decades:
- Devine Formula (1974): originally created for medication dosing, now widely used as a general ideal weight reference
- Robinson Formula (1983): a refinement of Devine’s approach
- Hamwi Formula (1964): one of the oldest, still commonly cited in nutrition education
- Miller Formula (1983): another variation with slightly different constants
All four follow a similar structure: a base weight for 5 feet of height, plus an additional amount for every inch above that.
The Devine Formula Explained
Men: 50 kg + 2.3 kg per inch over 5 feet Women: 45.5 kg + 2.3 kg per inch over 5 feet
Real Example: Woman, 5’6″
Let’s calculate.
- Height: 5’6″ = 66 inches = 6 inches over 5 feet
- Base weight: 45.5 kg
- Additional: 2.3 kg × 6 = 13.8 kg
Devine ideal weight: 45.5 + 13.8 = 59.3 kg ≈ 130.7 lbs
For comparison, the Hamwi formula for women uses 100 lbs for the first 5 feet, plus 5 lbs per inch above that:
Hamwi ideal weight: 100 + (5 × 6) = 130 lbs
Notice how close these two land — within a pound of each other for this example — even though they were developed roughly a decade apart using different methods.
Why These Formulas Were Never Meant for General Weight Advice
Here’s something most people don’t realize: the Devine formula was created for calculating medication dosages in clinical settings, not for telling healthy people what they should weigh. It became popular as a general reference almost by accident, since it was simple and widely available, not because it was validated for that specific purpose.
Limitations of Ideal Weight Formulas
- No account for muscle mass — a muscular, athletic person will often show as “overweight” by these formulas despite having a healthy body composition
- No account for frame size — someone with a larger bone structure naturally carries more healthy weight than someone with a smaller frame at the same height
- Based on outdated, limited populations — many of these formulas were developed using data that doesn’t reflect today’s more diverse population
- Single-number thinking — presenting one specific number implies more precision than these formulas actually offer; a healthy range makes more sense than a single target
The Mayo Clinic’s guidance on healthy weight recommends considering these formulas as rough starting reference points, not precise individual targets, and pairing them with other measures like waist circumference or body fat percentage for a fuller picture.
What Actually Matters More Than a Single Number
Rather than fixating on hitting one exact ideal weight figure, several other factors give a more complete health picture:
- Body fat percentage — as covered in our body fat calculator guide, this reflects composition rather than just total mass
- Waist circumference — a strong indicator of visceral fat and associated health risk, independent of overall weight
- How you feel functionally — energy levels, strength, and mobility often matter more day-to-day than matching a specific number
- Trends over time — the direction your weight is moving, and why, often carries more insight than any single snapshot figure
The CDC’s guidance on assessing weight status similarly emphasizes using multiple measures together rather than relying on any single formula in isolation.
Get your reference range across multiple formulas. Use the Ideal Weight Calculator →
Frequently Asked Questions
What is the most accurate ideal weight formula?
No single formula is definitively “most accurate,” since they were developed for different original purposes and use different assumptions. Most health professionals treat them as rough reference points rather than precise individual targets.
Why do ideal weight calculators give different results?
Each formula (Devine, Robinson, Hamwi, Miller) uses slightly different base weights and per-inch increments, developed at different times using different reference populations, which naturally produces somewhat different results for the same height.
Is ideal weight the same as healthy weight?
Not exactly. “Ideal weight” formulas produce a single reference number based on height alone, while “healthy weight” is a broader concept that also considers body composition, muscle mass, waist circumference, and overall health markers.
Should athletes use ideal weight formulas?
Generally no, or at least with heavy caution. Athletes and highly muscular individuals often weigh more than these formulas suggest due to muscle mass, which these calculations don’t account for, making the results misleading for that population.
What is a healthy weight range instead of one number?
Many health professionals prefer a healthy BMI range (typically 18.5–24.9) applied to your specific height, which produces a range rather than a single target, better reflecting the natural variation in healthy body types at the same height.
Do ideal weight formulas account for age?
No, the standard Devine, Robinson, Hamwi, and Miller formulas only factor in height and sex, not age, which is one of their notable limitations since healthy weight considerations can shift somewhat across different life stages.