Most people asking this want one number. The honest answer is that no formula can give you one, and the ones that claim to are all disagreeing with each other by ten pounds or more.
What you can get is a range — and a reasonable sense of where you sit inside it.
What Should I Weigh?
Four classic ideal-body-weight formulas next to the healthy BMI range for your height.
Methods: healthy range = BMI 18.5–24.9 at your height. Hamwi (1964), Devine (1974), Robinson (1983) and Miller (1983) are linear formulas built from mid-century insurance tables. They ignore frame size, muscle mass and age, so treat the spread as a range, never a single correct number.
Estimates only — general education, not medical advice. Talk with your doctor before changing how you eat or train. More tools at whatshouldiweigh.com.
Why there isn’t a single right number
Every formula that produces an “ideal” body weight takes two inputs: your height and your sex. That’s it. It doesn’t know whether you’re broad-shouldered or slight, whether you lift four times a week or haven’t trained in a decade, whether you’re 25 or 65.
Two men who are both 5 foot 10 get the identical answer from every one of these formulas. One of them might be a rugby player carrying 15% body fat. The other might be sedentary at 28%. The formula sees the same person.
That’s not a reason to ignore the number. It’s a reason to treat it as a starting point for a conversation rather than a verdict.
The healthy weight range
The most useful answer comes from body mass index, not from an ideal-weight formula. A BMI between 18.5 and 24.9 is classified as the healthy range for adults, and running that backwards gives you a span of weights rather than a point.
At 5 foot 6, that range runs from roughly 115 to 154 pounds. That’s a 39-pound spread, and all of it is inside the healthy band. Where you sit within it depends on how much muscle you carry, and muscle is heavy.
The four classic formulas
The calculator above runs all four side by side. They exist because different researchers, working from different data, arrived at different answers.
| Formula | Year | Originally built for |
|---|---|---|
| Hamwi | 1964 | Bedside nutrition counselling |
| Devine | 1974 | Calculating drug dosages |
| Robinson | 1983 | Revised drug dosing from newer data |
| Miller | 1983 | Revised again, from the 1983 insurance tables |
Notice what’s missing from that list: none of them were designed to tell a healthy adult what to weigh. Devine’s formula — still the most widely cited — was written so pharmacists could dose gentamicin in patients whose body weight would otherwise skew the calculation. It became a general health reference by accident.
They also disagree. For a man of 5 foot 10, Hamwi returns about 165 pounds and Miller returns about 155. Ten pounds apart, both described as “ideal,” neither wrong.
What none of them account for
Muscle mass. A pound of muscle and a pound of fat weigh the same and occupy very different space. Trained people frequently land above every ideal-weight formula while carrying less fat than someone below them.
Frame size. Hamwi’s original method adjusted by roughly 10% up or down for large and small frames. Most calculators, including this one, report the medium-frame figure.
Age. Some evidence suggests a slightly higher BMI is protective in older adults. The formulas don’t move with age.
Ethnicity. Health risk begins at lower BMI and waist thresholds in some populations — the WHO suggests different waist cut-points for Asian populations, for instance. A universal formula can’t reflect that.
Everything else. Bone density, limb proportions, fluid retention, medication, pregnancy, medical conditions.
How to actually pick a target
If you want something more useful than a number from a 1974 dosing formula, work through this instead:
1. Find your range, not your number. Use the healthy BMI span for your height as the outer boundary. Anywhere inside it is defensible.
2. Check your waist. Waist-to-height ratio predicts cardiometabolic risk better than BMI does, and it’s a single tape measurement. Keeping your waist under half your height is the rule of thumb. If your BMI reads high but your waist is well under that line, the BMI is probably picking up muscle.
3. Look at body composition, not just mass. Two people at the same weight can have very different amounts of fat. A tape measurement and the Navy method will get you closer than the scale will.
4. Think in direction, not destination. For most people the useful question isn’t “what should I weigh” but “is my weight trending in a direction I’m happy with, and am I getting stronger and fitter along the way?”
When the number matters less than you think
Weight is one input among several, and it’s the noisiest one. It moves two to four pounds across a single day on food volume, sodium, hydration and glycogen alone. Women see predictable swings across the menstrual cycle. Someone starting resistance training often holds weight steady for weeks while their body composition changes underneath.
If you’re weighing daily and reading each reading as a verdict, the signal you want is buried in noise. A weekly average tells you far more than any single morning does.
And the health markers that actually predict outcomes — blood pressure, resting heart rate, blood lipids, fasting glucose, how much you can lift, how far you can walk without stopping — respond to training and diet quality whether or not the scale cooperates. People improve every one of those while the number stays put.
Common questions
Is BMI accurate for me? It’s accurate as a population screening tool and imprecise for individuals. It doesn’t distinguish muscle from fat, and it wasn’t designed to. Pair it with a waist measurement for a better picture.
Why do the four formulas give different answers? Different source data and different decades. Hamwi worked from 1959 insurance tables, Miller from the 1983 revision. The spread between them is a fair illustration of how imprecise the whole exercise is.
Should I aim for the middle of the healthy range? Not necessarily. If you carry more muscle than average, the upper part of the range may suit you better. If you’re lightly built, the lower part. The range exists because there’s no single right point in it.
What if my goal weight falls below the healthy range? That’s worth discussing with a doctor or a registered dietitian rather than a calculator. Being below the healthy range carries its own risks — bone density, hormonal function, immune response — and no online tool is equipped to advise on it.
The calculators on this site are educational estimates, not medical advice. Talk with your doctor before making changes to how you eat or train.