Measurement · free tool
BMI Calculator
A ratio of weight to height. It is not a verdict on your health.
Your result
A ratio of weight to height. It is not a verdict on your health. Fill in the boxes and press Calculate — nothing is sent anywhere and no account is needed.
How this is worked out
- BMI = weight (kg) ÷ height (m)².
- The standard chart calls 18.5–24.9 the standard range, 25–29.9 above it and 30 or more well above it.
- There is nothing else in the equation. No body composition, no age, no sex, no distribution of fat, no training history.
Sources
- NHLBI/WHO body-mass-index categories. They were derived from population mortality data and were never intended to judge one person.
These are population equations. They describe averages well and individuals only roughly — which is what makes them a starting point rather than a prescription. Nothing here is medical advice.
The thinking
What BMI is actually for
What BMI is actually for
Adolphe Quetelet devised the ratio in the 1830s to describe the average build of a population. It was never intended to assess an individual, and it is still genuinely useful for what it was built for: comparing groups of people, cheaply, at scale.
It becomes misleading the moment it is pointed at one person. It has no way to know whether an extra ten kilograms is muscle or fat, and it has no way to know that two people with the same reading carry their weight completely differently.
Better questions than 'what is my BMI'
Has my waist measurement changed? Do the same clothes fit differently? Am I lifting more than I was two months ago? Am I sleeping, and do I have energy at four in the afternoon? Do the photographs from four weeks apart look different?
Those are the measures that move when training and nutrition are working, and they are the ones the Iron Katia progress hub tracks. None of them fits in a single ratio, which is precisely why the ratio is a poor answer.
Questions
Straight answers.
- Is BMI useless?
- Not useless — misapplied. It works at population scale, which is what it was built for. As a judgement on one person, especially one who trains, it is a poor instrument.
- My BMI says overweight but I lift. What now?
- Almost certainly nothing. Muscle is dense; the equation cannot see it. Judge by measurements, photographs and performance instead.
- What should I track instead?
- Waist and hip measurements, monthly photographs in the same conditions, strength on your main lifts, and how you sleep and feel. Weight is worth logging as a trend line, not as a daily verdict.
Keep going
One number is a reading. A trend is progress.
Every calculator here gives you a starting point and nothing more. What turns it into something useful is logging what you actually do against it — which is free, takes a minute a day, and is where the 14-day START HERE challenge begins.
Start freeNo card, no plan. Or see what coaching adds.