Ideal Weight Calculator Guide 2026: BMI, IBW Formulas & Frame Size Compared
"How much should I weigh?" is one of the most searched health questions online. The honest answer: it depends. Your ideal weight isn't a single number — it's a range determined by your height, sex, age, frame size, and body composition. A 180-lb person with 15% body fat is in a very different health position than a 180-lb person with 35% body fat, even at the same height.
This guide compares the five most commonly used ideal body weight (IBW) formulas, explains how frame size affects your target, and shows why a healthy weight range is more useful than a single magic number.
TL;DR
There are 5 major ideal weight formulas (Devine, Robinson, Miller, Hamwi, and BMI-based range). They all follow the pattern "base weight + increment per inch over 5 feet" but produce results that can vary by 10–15 lbs. The most practical approach: calculate with multiple formulas, adjust ±10% for frame size, and treat the result as a range rather than a target. A BMI between 18.5 and 24.9 defines the "normal weight" range per WHO guidelines.
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The 5 Ideal Body Weight Formulas Compared
All five major IBW formulas use the same basic structure: a base weight for someone who is exactly 5 feet tall, plus an increment for each additional inch of height. They differ in the constants used, producing a spread of results. Here are the formulas and what they yield for a 5'10" man and a 5'4" woman:
| Formula | Year | Men (per inch over 5') | Women (per inch over 5') |
|---|---|---|---|
| Devine | 1974 | 50 kg + 2.3 kg/in | 45.5 kg + 2.3 kg/in |
| Robinson | 1983 | 52 kg + 1.9 kg/in | 49 kg + 1.7 kg/in |
| Miller | 1983 | 56.2 kg + 1.41 kg/in | 53.1 kg + 1.36 kg/in |
| Hamwi | 1964 | 48.0 kg + 2.7 kg/in | 45.5 kg + 2.2 kg/in |
| BMI Range | WHO | BMI 18.5–24.9 | BMI 18.5–24.9 |
Worked Example: 5'10" Male and 5'4" Female
Here's what each formula produces for two common heights. Notice the spread between the lowest and highest result — this illustrates why a single "ideal weight" number is misleading.
Man — 5'10" (70 inches)
Woman — 5'4" (64 inches)
These formulas produce a 10-lb spread for the man and a 9-lb spread for the woman at the same height. Neither the highest nor the lowest is "wrong" — the entire range is a reasonable target. Using all five formulas gives you a practical band rather than an unrealistically precise number.
How Does Frame Size Affect Your Ideal Weight?
Bone structure varies significantly between individuals. A person with a large skeletal frame (wider wrists, broader shoulders, thicker bones) naturally weighs more than someone of the same height with a small frame — even at identical body fat levels. The standard adjustment is ±10%: subtract 10% from your IBW for a small frame, add 10% for a large frame.
You can estimate frame size using the wrist circumference method. Measure around your dominant wrist just below the wrist bone:
| Frame Size | Men (Wrist) | Women (Wrist) | IBW Adjustment |
|---|---|---|---|
| Small | Under 6.5" | Under 5.5" | −10% |
| Medium | 6.5"–7.5" | 5.5"–6.5" | No change |
| Large | Over 7.5" | Over 6.5" | +10% |
Example: A 5'10" man with a Devine IBW of 161 lbs and a large frame (wrist over 7.5") would adjust to 161 × 1.10 = 177 lbs. This makes the IBW more realistic for his skeletal build.
BMI Range vs. Single-Number IBW: Which Is Better?
The IBW formulas give you a single number. The BMI-based approach gives you a range. For most people, the BMI range is more practical because it acknowledges that health isn't a point on a scale — it's a zone.
IBW Formulas (Single Number)
- Pro: Simple, memorable target
- Pro: Used in clinical settings for drug dosing
- Con: Implies false precision — health is not one number
- Con: Developed decades ago on limited populations
BMI Range (18.5–24.9)
- Pro: Acknowledges healthy weight is a range
- Pro: Based on WHO epidemiological data
- Con: Doesn't distinguish muscle from fat
- Con: May overestimate risk for muscular individuals
For a 5'10" man, the BMI "normal weight" range is 129–174 lbs. That's a 45-lb band — much wider and more realistic than any single IBW formula. The midpoint (BMI 22) is 153 lbs, close to what the formulas produce. The range approach accommodates different frame sizes, muscle mass, and body types.
Our recommendation: Use the IBW formula range (from all 5 formulas) as your initial reference, adjust ±10% for frame size, then validate against the BMI normal range. If your weight falls within both zones and your metabolic markers (blood pressure, blood sugar, cholesterol) are healthy, you're likely in good shape.
Limitations of Ideal Weight Calculators
Every ideal weight formula has blind spots. Understanding these limitations prevents setting unhealthy or unrealistic targets.
Body composition is invisible
None of these formulas account for muscle mass vs. fat mass. A resistance-trained athlete with 15% body fat may weigh 20+ lbs above their Devine IBW and be perfectly healthy.
Age is not factored
Healthy weight tends to increase slightly with age. A 25-year-old and a 65-year-old at the same height will have different optimal weights. Research in the Journal of the American Geriatrics Society suggests slightly higher BMIs (23–27) are associated with lower mortality in older adults.
Ethnicity differences exist
These formulas were developed primarily on Western populations. The WHO recommends different BMI thresholds for Asian populations (overweight at 23, not 25) due to higher metabolic risk at lower BMIs.
Mental health impact
Fixating on a single target weight can contribute to disordered eating patterns. Health organizations increasingly recommend focusing on behaviors (activity, nutrition quality) rather than a number on the scale.
Frequently Asked Questions
What is the most accurate ideal weight formula?
No single formula is universally most accurate. The Devine formula (1974) is most used clinically. For general health, the BMI-based range (18.5–24.9) is more realistic. Best approach: compare all five formulas and use the range, adjusted for frame size.
How much should I weigh for my height?
It depends on sex, frame size, and body composition. A 5'8" man's ideal weight ranges from about 139–164 lbs across formulas. A 5'4" woman's ranges from 108–145 lbs. These are starting references — metabolic health markers matter more than an exact number.
What is the Devine formula?
Devine (1974): Men = 50 kg + 2.3 kg per inch over 5 feet. Women = 45.5 kg + 2.3 kg per inch over 5 feet. Originally developed for medication dosing, it's the most commonly referenced IBW formula in clinical practice.
Does frame size affect ideal weight?
Yes. Large-framed individuals should add about 10% to their IBW estimate; small-framed individuals should subtract 10%. Frame size is estimated by wrist circumference: under 6.5" (men) or under 5.5" (women) indicates a small frame.
Why do different calculators give different ideal weights?
Each formula was developed for different purposes using different populations. Devine (1974) for drug dosing, Robinson (1983) for clinical nutrition, Hamwi (1964) for diabetes dietary planning. Results can vary by 10–15 lbs for the same person — which is why using a range is more practical.