A 32-year-old male, 176 cm, 78 kg. The BMI calculator returns 25.2. According to the World Health Organization, that is overweight. One decimal point above the 24.9 cutoff.
But plug the same height into three ideal-weight formulas and the picture changes. Broca says 68.4 kg. Devine says 71.4 kg. Robinson says 69.7 kg. Average those, adjust for a medium frame, and the optimal midpoint lands at 69.8 kg with a range stretching up to 76.8 kg. So 78 kg is only 1.2 kg above the top of the ideal range - not the alarming "overweight" label that BMI assigns.
Which number do you trust? The answer depends on what question you are actually asking.
The 25.0 line that changes everything
BMI divides weight by height squared. Nothing more. It does not know whether those 78 kilograms are muscle, fat, water or bone. It does not care about waist circumference, body fat percentage or how many push-ups you can do.
The BMI Calculator classifies results into eight WHO categories. Here is where the boundaries fall:
| Category | BMI range | What it means in practice |
|---|---|---|
| Underweight | < 18.5 | Potential nutrient deficiency, hormonal disruption |
| Normal weight | 18.5 - 24.9 | Statistically lowest risk of chronic disease |
| Overweight | 25.0 - 29.9 | Increased risk, but highly dependent on body composition |
| Obesity class I | 30.0 - 34.9 | Elevated risk of type 2 diabetes, hypertension |
The healthy weight range for someone 176 cm tall runs from 57.3 kg to 77.1 kg. Our 78 kg subject misses the upper boundary by less than a kilogram. That gap - 0.9 kg - could be a glass of water, a meal, or the difference between weighing yourself at 7 AM versus 9 PM.
BMI was designed in 1832 by Adolphe Quetelet for population-level statistics. It was never meant to diagnose an individual. But it stuck because the formula is simple, the inputs are easy to collect, and the thresholds are easy to remember.
1,725 calories just to stay alive
Knowing your weight category is one thing. Knowing how many calories your body actually needs is another.
The BMR & TDEE Calculator uses the Mifflin-St Jeor equation - the most accurate predictive formula for basal metabolic rate in healthy adults. For our 78 kg, 176 cm, 32-year-old male:
- BMR (lying still all day, doing nothing): 1,725 kcal
- TDEE (moderately active, training 3-5x/week): 2,674 kcal
- Cutting target (-500 kcal deficit): 2,174 kcal
The macro split at 2,174 kcal: 156 g protein (2g per kg), 60 g fat (25% of calories), 253 g carbs (the remainder).
A 500 kcal deficit translates to roughly 0.45 kg per week. At that rate, dropping from 78 to 77 kg takes about two weeks. Enough to slide from "overweight" back into "normal" on the BMI scale. Whether that actually matters for health is a different conversation.
| Activity level | Multiplier | TDEE at 1,725 BMR |
|---|---|---|
| Sedentary (desk job) | 1.2 | 2,070 kcal |
| Lightly active (1-2x/week) | 1.375 | 2,372 kcal |
| Moderately active (3-5x/week) | 1.55 | 2,674 kcal |
| Very active (6-7x/week) | 1.725 | 2,976 kcal |
| Extremely active (2x/day) | 1.9 | 3,278 kcal |
The gap between sedentary and very active is over 900 kcal. That is an entire meal. Most people overestimate their activity level - if you sit at a desk 8 hours and hit the gym three times a week, you are closer to "lightly active" than "moderately active."
Three formulas, three opinions
This is where it gets interesting. BMI gives you a category. Ideal weight formulas give you a target. And they rarely agree with each other.
The Ideal Weight Calculator runs Broca (1871), Devine (1974) and Robinson (1983) simultaneously. For a 176 cm male with a medium frame:
| Formula | Ideal weight | How it calculates |
|---|---|---|
| Broca | 68.4 kg | (height - 100) x 0.9 |
| Devine | 71.4 kg | 50 + 2.3 x (inches over 60) |
| Robinson | 69.7 kg | 52 + 1.9 x (inches over 60) |
| Average | 69.8 kg | Mean of all three |
| Range | 62.8 - 76.8 kg | Average +/- 10% |
Broca is the oldest and simplest. It tends to run low for taller people. Devine was designed for drug dosing in pharmacology - not for telling someone their goal weight. Robinson refined Devine's coefficients slightly.
The practical takeaway: averaging all three gives a more balanced estimate than relying on any single one. And the range matters more than the midpoint. A 176 cm male can weigh anywhere from 62.8 kg to 76.8 kg and still fall within the ideal zone.
Compare that to the BMI-based range: 57.3 - 77.1 kg. The overlap is large, but the ideal weight formulas suggest a narrower, higher band. At 78 kg, BMI says overweight. The ideal weight range says you are 1.2 kg above the top end. The difference in framing is significant.
So which number wins?
None of them. They answer different questions.
BMI answers: "Where does this person fall on a population-level risk curve?" It is useful for screening, not diagnosis. A muscular 90 kg athlete at 180 cm has a BMI of 27.8 (overweight) with 12% body fat.
BMR/TDEE answers: "How many calories does this body need?" It tells you what to eat, not what to weigh. A person with a BMI of 24.9 and one with 25.1 have nearly identical caloric needs.
Ideal weight formulas answer: "What weight range makes clinical sense for this height and frame?" They are conservative estimates from an era when the average person was shorter and less muscular than today.
The real indicators of metabolic health - waist circumference, blood pressure, fasting glucose, lipid panel - do not appear in any of these calculators. But these three tools give you a starting framework. Run your numbers. Compare the results. Then talk to a doctor who can look at the full picture.
Tools discussed in this article
BMI Calculator - calculate your Body Mass Index from height and weight, get WHO classification into eight categories from severe thinness to class III obesity, and see the healthy weight range for your height.
BMR & TDEE Calculator - find your Basal Metabolic Rate and Total Daily Energy Expenditure using the Mifflin-St Jeor formula, with target calories for cutting, maintenance or bulking and a protein/fat/carb macro split.
Ideal Weight Calculator - compare your ideal weight across three clinical formulas (Broca, Devine, Robinson), adjusted for sex, body frame and age, with a realistic range instead of a single number.
Check for a specific value
- BMI at 70 kg - normal or overweight
- BMI at 90 kg - weight assessment
- Ideal weight 170 cm - healthy range
- Ideal weight 180 cm - target weight
- WHR waist 85 cm - visceral fat risk