Ideal Weight for Muscular People — Why the Formulas Get It Wrong

Run your stats through an ideal weight formula and it might tell you that you're 10–20 kg overweight. If you train regularly and carry significant muscle mass, that number is almost certainly wrong — not because you're special, but because the formulas weren't built with you in mind.

The Ideal Weight Calculator shows results from multiple formulas (Hamwi, Devine, Robinson, Miller) alongside each other. For most people, comparing those outputs gives a useful range. For muscular people, all four tend to land below a realistic healthy weight. Here's why.

What the Formulas Were Actually Designed For

The Hamwi, Devine, Robinson, and Miller formulas were all developed between 1964 and 1983 — not as fitness targets, but as clinical reference tools. Their original purpose was to help medical professionals estimate lean body mass for drug dosing calculations. Gentamicin, an antibiotic, was one of the main use cases: the dose is calculated based on lean body weight, not total body weight, because the drug doesn't distribute well into fat tissue.

For that purpose — estimating lean mass in average, untrained patients — the formulas work reasonably well. They use height and sex as proxies for frame size and natural body composition. But they were calibrated on hospital patient populations in mid-20th century America, not on trained athletes or people who have built significant muscle mass over years.

There's no adjustment in any of these formulas for muscle. They assume a relatively fixed relationship between height and healthy weight that simply doesn't hold when someone has added 10–15 kg of lean mass through training.

Why Muscle Mass Breaks the Formula

Consider a man who is 5'10" (177 cm). The Devine formula gives an ideal weight of 50 + (2.3 × 10) = 73 kg. The Robinson formula gives 52 + (1.9 × 10) = 71 kg. Average the four formulas and you get somewhere around 73–75 kg.

Now consider that a 5'10" man who has trained seriously for several years might have a lean body mass — muscle, bone, organs, water — of 75–80 kg on its own. Adding even a modest, healthy amount of body fat (say, 12–15%) brings total weight to 85–92 kg. The formula says 73 kg. The reality is that 90 kg is entirely healthy for this individual.

That's not a rounding error. That's 15–20 kg off, and the formula has no mechanism to account for it.

The same issue affects women, though the numbers are smaller in absolute terms. A 5'6" woman who lifts consistently and has built meaningful muscle mass will often weigh 10–15 kg more than the formula output without any excess fat.

BMI Has the Same Problem — and Then Some

Body Mass Index divides weight by height squared. It was invented by Adolphe Quetelet in the 19th century as a population-level statistical tool — he was a mathematician studying averages, not a clinician trying to assess individual health.

For a 5'10" man at 90 kg, BMI is 28.9 — solidly in the "overweight" category. For someone with 12% body fat at that weight, the classification is absurd. The BMI Calculator will tell you the number, but it should be read alongside body fat percentage, not as a standalone verdict.

The well-documented failure of BMI for muscular individuals is exactly why tools like the Body Fat Calculator exist. A body fat percentage reading gives you information BMI can't: the actual ratio of fat to lean mass. A muscular person at 90 kg with 12% body fat and a sedentary person at 78 kg with 28% body fat might have similar BMIs but wildly different health profiles.

What to Use Instead

For muscular people, ideal weight formulas and BMI are at best a starting point and at worst actively misleading. More useful measures:

Body fat percentage. This is the most direct measure of body composition. For men, 10–20% is a healthy and sustainable range for most active people; 6–13% is athletic. For women, 18–28% is a healthy active range; 14–20% is athletic. If your body fat is in a healthy range, your weight is appropriate — regardless of what a formula says.

Waist circumference. Abdominal fat is the clinically relevant risk factor in most metabolic conditions. A waist measurement under 94 cm for men and 80 cm for women is associated with low metabolic risk. Under 102 cm (men) and 88 cm (women) is associated with moderate risk. A muscular person at "overweight" BMI with a 85 cm waist has a fundamentally different risk profile than someone with a 102 cm waist at the same BMI.

Waist-to-height ratio. Divide waist circumference by height. A ratio below 0.5 is associated with lower cardiovascular risk. This measure is less affected by muscle mass than BMI because muscle doesn't preferentially accumulate around the waist.

How you feel and perform. This sounds unscientific but it's actually important. If you're sleeping well, recovering from training, not experiencing hormonal disruption, and your bloodwork (cholesterol, blood glucose, blood pressure) is normal, a number above the "ideal" formula range is not a health problem.

What "Ideal Weight" Actually Means for Someone Who Trains

For trained individuals, a more realistic target is to aim for a body fat percentage that falls in the athletic or fitness range for your sex, at whatever total weight that implies.

For a 5'10" man with significant muscle mass, that might be 85–95 kg at 10–15% body fat. For a 5'6" woman who lifts, it might be 65–75 kg at 18–24% body fat. These are healthy weights — they're just not what the Hamwi formula returns.

The formula outputs are still worth knowing. They represent roughly what the average untrained person at your height might weigh at a healthy composition. If your weight is substantially above the formula range, it's worth verifying your body fat percentage is actually in a healthy zone rather than assuming it's all muscle. But being 15 kg above the formula output while at 12% body fat is not a problem to fix.

When to Take the Formula Seriously

The formula output does matter in one situation: if your weight is above the ideal range and you haven't built significant muscle mass through consistent training. If you've been mostly sedentary and the formula says you're above your ideal weight, that's worth investigating — the weight is more likely to be fat than muscle.

The way to distinguish between these scenarios is to measure body fat. The Body Fat Calculator uses the US Navy tape method — circumference measurements at the waist, neck, and hips — to estimate body fat percentage without any equipment beyond a tape measure. That reading tells you what the formula can't.

For setting realistic weight and composition goals, combining the ideal weight output with a body fat estimate and a TDEE calculation from the TDEE Calculator gives you a complete picture: where you are, where a reasonable target is, and how many calories support getting there while maintaining muscle.

The Practical Answer

If you train seriously, the ideal weight formula number is not your target. It's a reference point for what an untrained person your height might weigh at healthy body composition. Your actual healthy weight is whatever produces a body fat percentage in the healthy or athletic range for your sex — and for someone with meaningful muscle mass, that will almost always be higher than the formula suggests.

Use the Ideal Weight Calculator to see all four formula outputs. Then compare that range against your body fat percentage. The gap between the formula output and your actual healthy weight is a reasonable estimate of how much lean mass you've added above baseline — and for someone who trains consistently, that's something to maintain, not to reduce.