The first time I typed my height into an "ideal weight calculator" online, I got a number that made me laugh out loud.
According to the formula, I should weigh somewhere between 128 and 160 pounds. I'm a 5'11" guy who played college rugby and has been lifting weights for over a decade. At my leanest — genuinely lean, visible abs, the whole thing — I weighed 181 pounds. The calculator's ceiling was 21 pounds below that.
I assumed the calculator was broken. Then I tried three more. Same ballpark every time.
That sent me down a rabbit hole I wasn't expecting. What are these formulas actually based on? Who built them, and for whom? And is there a version of "ideal weight" that means something useful for a real person trying to make real health decisions?
Here's what I found.
The Formulas That Get Used Most
There isn't one universal "ideal weight" formula. There are several, each developed at different times, by different people, for different purposes — and they give different answers for the same person.
The Devine Formula is probably the most widely used, especially in clinical settings. It was published in 1974 by Dr. B.J. Devine, originally to calculate medication dosages — not to define a healthy weight target. For men, it starts at 50kg for 5 feet of height and adds 2.3kg for every inch above that. For women, it starts at 45.5kg and adds the same increment.
Plug in 5'11" and you get about 70kg, or roughly 154 pounds for a man. That's the formula that told me I should weigh 27 pounds less than I do at peak fitness.
The Hamwi Formula is similar and often used in dietitian practice. For men: 106 pounds for the first 5 feet, then 6 pounds per inch above that. For women: 100 pounds for 5 feet, then 5 pounds per inch. At 5'11", that puts a man at 172 pounds — a bit more reasonable, but still a single number with no room for body composition, frame size, or muscle mass.
The Robinson Formula (1983) and the Miller Formula (1983) are two others that get referenced. They use slightly different multipliers and produce slightly different results. If you've ever used a "compare multiple ideal weight formulas" calculator online and wondered why they all show different numbers, that's why — they're literally different equations.
What all of these formulas have in common: they were developed primarily from data on white European populations, mostly men, and their goal was clinical utility (dosing medications, predicting organ sizes) rather than defining what anyone should actually weigh for health.
None of them account for muscle mass, bone density, fat distribution, age, ethnicity, or fitness level.
Why a Single Number Is the Wrong Way to Think About This
I talked to a sports dietitian about this after my calculator rabbit hole, and she made a point that reframed the whole thing for me.
She said: "Ideal weight isn't a number on a scale. It's a range, and the range depends on your body composition — specifically how much of your weight is fat versus everything else."
That hit differently than a formula.
Two people can weigh exactly the same and be in completely different health situations. A 175-pound person who is 28% body fat has a very different physiological profile than a 175-pound person who is 16% body fat — same scale number, very different picture.
This is the same problem that makes BMI imperfect (weight-to-height ratio tells you nothing about what the weight is made of), and it's the same problem with single-number ideal weight formulas. They're measuring weight as a proxy for something they actually care about — body composition and metabolic health — but the proxy is imprecise.
The Body Composition Approach: More Useful, Slightly More Work
If you want a target that actually means something for your body specifically, you need to think about body composition rather than total weight.
Here's a practical way to do this:
Step 1: Get an estimate of your current body fat percentage.
You don't need a DEXA scan to start (though that's the most accurate option). Reasonable estimates are available from:
- Smart scales using bioelectrical impedance — brands like Withings Body+, Tanita, or the more affordable Eufy Smart Scale. These aren't lab-accurate but are useful for tracking trends. Consistent measurement conditions matter: same time of day, same hydration state.
- Calipers — old school but functional. The 3-site or 7-site skinfold method done by a trainer or sports medicine professional is reasonably accurate.
- Navy body fat formula — uses neck and waist measurements (and hip for women) to estimate body fat percentage. Free calculators for this are all over the internet, and while it's not precise, it's a decent ballpark without any equipment beyond a measuring tape.
Step 2: Calculate your lean body mass.
Lean body mass (LBM) is everything that isn't fat — muscle, bone, organs, water. If you weigh 180 pounds and you're 20% body fat, your fat mass is 36 pounds and your lean body mass is 144 pounds.
The formula: LBM = Total Weight × (1 − Body Fat Percentage as a decimal)
Step 3: Set a target body fat percentage, not a target weight.
General reference ranges for body fat (these vary somewhat by source, but these are commonly cited benchmarks):
For men:
- Essential fat: 2–5%
- Athletic: 6–13%
- Fitness: 14–17%
- Acceptable: 18–24%
- Obese: 25%+
For women:
- Essential fat: 10–13%
- Athletic: 14–20%
- Fitness: 21–24%
- Acceptable: 25–31%
- Obese: 32%+
Pick a target range that makes sense for your age, lifestyle, and goals. Someone who wants to run a 5K and feel good at 45 has different needs than someone training for a physique competition.
Step 4: Back-calculate a realistic target weight.
If your lean body mass is 144 pounds and you want to reach 15% body fat, the math is:
Target Weight = LBM ÷ (1 − Target Body Fat) Target Weight = 144 ÷ 0.85 = approximately 169 pounds
That's your target — built from your actual body, not a formula that was designed for medication dosing in the 1970s.
What I Actually Use to Track This
After going through all of this myself, here's the setup I landed on:
A Withings Body+ scale at home that measures weight and gives a bioelectrical impedance body fat estimate every morning. I log it in the Apple Health app automatically. I know the body fat readings bounce around based on hydration, so I look at the 30-day trend rather than any individual data point.
Every six months or so I get a DEXA scan at a local sports performance clinic — in most cities you can find these for $50–$100 now, and they give highly accurate breakdowns of body fat, lean mass, and even bone density by body region. Having that anchor point makes my at-home scale readings more interpretable.
I don't obsess over the scale number anymore. I care more about whether my lean mass is stable or growing and whether my body fat percentage is moving in the right direction.
Mistakes I Made (And Still See Everywhere)
Using ideal weight as a goal weight. Early on I set weight loss goals based on "what I should weigh" according to a formula. Those numbers were disconnected from my actual body. I've seen this derail people repeatedly — they hit the formula's target and feel worse than when they started because they lost muscle along with fat, or they never reach the target because it's physiologically unrealistic for their frame and muscle mass.
Conflating healthy weight with a specific appearance. The range of body compositions that support good health is wider than fitness media suggests. People live long, healthy lives at a variety of body fat percentages, and the relationship between aesthetics and health is a lot more complicated than "look lean, be healthy."
Ignoring the frame size variable. Most ideal weight formulas offer a rough adjustment for "small," "medium," and "large" frame — usually measured by wrist circumference. It's a crude correction, but it acknowledges something real: skeletal frame size affects healthy weight range. A person with a larger bone structure will naturally carry more weight for the same height. Most calculators you find online skip this entirely.
Chasing a number on a deadline. Weight changes tied to rigid timelines and specific numbers tend to produce short-term results via methods (severe restriction, extreme cardio) that aren't sustainable. The most useful target weight is the one you can maintain without misery — which takes some experimentation to actually find.
A Practical Starting Point
If you want a number to work with and you're not ready to dive into body composition math, here's a reasonable middle ground:
Take the Hamwi formula result. Then add 10% if you're naturally large-framed or carry significant muscle mass, and subtract 5% if you're small-framed and sedentary. Use that as the center of a 10-pound range, not a hard target.
Then spend four to six weeks paying more attention to how you feel, how your clothes fit, your energy levels, and your performance in physical activity than to what the scale says on any given morning.
The number you're looking for isn't the one a formula gives you. It's the one where your body functions well, you can sustain your habits without constant effort, and you feel like yourself. That's a range, and it shifts throughout your life.
The formulas are starting points for a conversation — with yourself, and ideally with a doctor or registered dietitian who can look at your actual bloodwork and history. They're not the final word, and they were never meant to be.