Your ideal body weight is a range, not a number. The classic formulas — Devine, Hamwi, Miller, Robinson — were built for drug dosing and life-insurance tables, not for setting personal weight goals. For most adults, the useful target is a BMI-based weight window roughly 30–40 pounds wide, cross-checked against waist circumference and body fat. Let’s look at where these formulas came from, why they argue with each other, and what you can actually do with that info.
What “ideal body weight” actually means
Ideal body weight (IBW) is a weight range associated with lower health risk for a given height and sex, not a precise fixed target. The four formulas most people encounter — Devine (1974), Hamwi (1964), Miller (1983), Robinson (1983) — were not designed to answer “what should I weigh for health.”
A 2000 review in the Annals of Pharmacotherapy traced their origin: height-weight tables were built to compare populations, those tables correlated with mortality, and the word “ideal” attached itself to the middle of the distribution. Devine’s equation entered clinical practice because drug pharmacokinetics lined up with IBW. It did not define what an “optimal” body should weigh. The formulas still show up in dosing worksheets. They were never personal prescriptions.
For a 5′9″ adult, the BMI 18.5–24.9 window translates to roughly 125–168 lb. That 43-pound spread is closer to what “ideal” should mean than any single formula output.
Four formulas, one 18-pound spread
Run the numbers for the same height and the disagreement becomes obvious. For a 5′10″ man, Devine gives 161 lb, Hamwi 165 lb, Miller 147 lb, Robinson 156 lb. An 18-pound gap between the lowest and highest “ideal.”
| Formula | Year | 5′10″ male | 5′5″ female | Original context |
|---|---|---|---|---|
| Devine | 1974 | 161 lb | 125 lb | Drug dosing (gentamicin) |
| Hamwi | 1964 | 165 lb | 125 lb | Clinical quick estimate |
| Miller | 1983 | 147 lb | 117 lb | Clinical nutrition |
| Robinson | 1983 | 156 lb | 120 lb | Drug dosage calculations |
None is “correct.” The spread is the finding. A 5′5″ woman reading these four formulas gets targets between 117 and 125 lb — eight pounds apart — and none of those numbers knows whether she lifts weights, has a wide frame, or carries more visceral fat than her scale suggests.
We had to drop the old Hamwi table from a calculator tooltip last year. Returning users kept asking why the number it spat out didn’t match the range our BMI tool displayed on the same page. Two sources of truth on one screen is worse than none.
Why waist and body fat matter more than the formula
NHLBI draws the waist line at 35 inches for women and 40 inches for men: above those thresholds, heart disease and type 2 diabetes risk rises regardless of what the scale says. That is a stronger screening signal than a formula output because it measures where fat actually sits, not just how much mass the body carries.
Body composition adds the second layer. Federal guidance notes that BMI and waist size don’t directly measure the amount of body fat, and that some people with lower BMI and waist readings still carry elevated risk. A 5′10″ man at 175 lb with 15% body fat is metabolically different from a sedentary man at 160 lb with 30% body fat, even though the lighter man is “closer to ideal” by every formula in the table above.
Waist: under 35 inches (women) / 40 inches (men).
Body fat: commonly cited healthy ranges run roughly 14–17% for men and 21–24% for women in midlife, shifting with age.
Trend matters as much as the single reading. A stable waist across 6–12 months tells you more than one low weight recorded on a good morning.
How to build your range in three moves
Start with the BMI window for your height. For 5′8″, that is roughly 122–164 lb. For 5′4″, roughly 108–145 lb. The exact numbers matter less than the width — a 40-pound band leaves room for frame, muscle, and age without pretending one point inside it is “correct.”
Adjust inside the band rather than replacing it. A small frame or a lifelong stable weight sits toward the lower half. A large frame, a history of resistance training, or an age above 65 pushes toward the upper half — and in some cases slightly above BMI 24.9 if waist and body fat stay in range. Federal research notes that older adults often carry more fat at the same BMI as muscle mass declines, which is one reason the scale alone becomes less informative with age.
Then set a target you can actually hold. If you are currently above the BMI window, a 5–7% loss is the evidence-backed first step: CDC data show that magnitude of weight loss cuts type 2 diabetes incidence by 58% in adults with prediabetes, rising to 71% for those over 60. That is a smaller and more defensible goal than chasing the lowest formula output.
One reader example stayed with us. A 5′6″ woman spent years trying to hit the Hamwi number for her height, then found she felt best about 12 pounds higher, with a 31-inch waist and consistent strength training. Her blood markers were in range. The formula had been telling her the wrong thing for a decade.
Where the standard range needs adjusting
For Asian adults, WHO’s 2004 expert consultation recommends lower action points: overweight begins at BMI 23.0 and obesity at 27.5, because metabolic risk appears at lower BMI values in many Asian populations. An asian bmi calculator applies those lines instead of the global 25/30 table.
For adults over 65, the mortality-optimal BMI sits higher than 18.5–24.9. A meta-analysis of 32 prospective cohorts covering nearly 198,000 adults over 65 found the lowest all-cause mortality at BMI 27.0–27.9, while BMI 19.0–19.9 carried a 28% higher risk. Multiple large cohort studies put this lower-risk band around 23–28. The practical implication is not “gain weight after 65” — it is that a BMI of 21 at 75 does not carry the same reassurance it does at 35.
Before recalculating anything, measure your waist. Then run your height and weight through a Free BMI Calculator to see which band you land in. If the number and the tape disagree, the tape usually has the more useful answer.
Frequently Asked Questions
What is the most accurate ideal body weight formula?
None of them is “most accurate” for personal weight goals, because none was designed for that purpose. Devine is the most common in clinical settings for drug dosing, but a BMI-based weight range cross-checked with waist circumference is a more defensible starting point for health purposes.
Does ideal body weight change with age?
Yes. The BMI linked to lowest mortality tends to shift upward after 65, and body composition changes mean the same weight represents more fat and less muscle than it did at 30. A formula number derived from a 1970s height-weight table does not account for either shift.
I’m muscular and my BMI says overweight. Should I use these formulas?
No. Regular strength training builds extra muscle. That extra bulk will make standard IBW and BMI numbers misleading. Use waist circumference, body fat percentage, and performance trends instead. An athlete bmi calculator can show how the standard bands shift for trained bodies.
Should I set a calorie goal based on my ideal weight?
No. Set calories from your current weight, then apply a moderate deficit if weight loss is the goal. Two reasons this matters:
Eating for a weight you do not yet have creates a deficit large enough to be unsustainable.
The rebound from that deficit usually erases the loss within months.
What if my ideal weight by formula is lower than I can maintain?
Then the formula is not your ideal. A weight you can hold for years with reasonable eating and activity is a better health target than a lower number you regain in six months. Most people we hear from feel better somewhere in the middle third of their range, not at the bottom edge.
Sources
NHLBI: Aim for a Healthy Weight — Waist Circumference and Health Risk
CDC: National Diabetes Prevention Program — 5–7% Weight Loss and Type 2 Diabetes Incidence
This article is for informational and educational purposes only. It does not constitute medical advice or replace professional health assessment. Always consult a qualified healthcare provider regarding your individual health and weight-related goals. Individual results will vary. The BMI Calculator Blog Team maintains editorial independence and does not sell health products.
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Last updated: October 18, 2026.