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BMI calculator

Q: What is BMI?

BMI (Body Mass Index) is your weight divided by your height squared. It's a quick, population-level screening number used by health organizations, but it doesn't distinguish between muscle and fat — it only knows total weight.

Q: Is BMI accurate for muscular people?

No. BMI can't tell the difference between muscle and fat, so a heavily muscled, lean person can score as 'overweight' or 'obese' on BMI despite having very little body fat. It was designed as a population-level statistical tool, not an individual body-composition measurement.

Q: What is a normal BMI range?

The standard WHO reference ranges are: under 18.5 is classified underweight, 18.5-24.9 normal, 25-29.9 overweight, and 30+ obese. These are population screening categories, not individual health verdicts.

Q: What should I use instead of BMI if I lift weights?

FFMI uses estimated fat-free mass rather than total body weight, but fat-free mass includes more than skeletal muscle and depends on a body-fat estimate. It can help answer a different question from BMI; neither measures physique or health on its own. A photo-based grade is a visual estimate, not a body-composition measurement.

Instant, free, no signup. And below it: the honest part most BMI calculators skip — what this number actually can and can't tell you.

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What BMI actually measures

BMI is weight in kilograms divided by height in metres squared. It is a screening measure of weight relative to height; it does not directly measure body fat or distinguish fat, muscle and bone. The CDC recommends interpreting BMI for an individual alongside other information.

A person with more muscle can have a higher BMI without that number showing what their body weight is made of. BMI remains useful as a screening and population measure, but it cannot answer an individual body-composition question by itself.

Where it has limits

Two people with the same height and weight have the same BMI, even if their body composition differs. The formula has no input for fat mass, muscle mass or where fat is distributed. The CDC notes that BMI cannot distinguish fat, muscle and bone mass.

No muscle vs. fat distinction — the single biggest blind spot, and the one that matters most if you train.
No frame or distribution awareness — where the weight sits on you isn't part of the equation.
A screening measure — useful in population health and as one piece of individual screening, but not a standalone assessment of one person's body composition or health.

Standard BMI ranges

<18.5Underweight — WHO reference category.

18.5–24.9Normal — WHO reference category.

25–29.9Overweight — WHO reference category.

30+Obese — WHO reference category.

These adult reference categories are published by the World Health Organization. They are population screening ranges, not an individual diagnosis, and do not account for muscle mass or frame.

What to use instead, if you lift

If BMI does not answer the question you have, the FFMI calculator uses estimated fat-free mass instead of total body weight. Fat-free mass includes more than skeletal muscle, and its estimate depends on body-fat input. A photo-based grade offers a separate visual read of visible areas; it does not measure body composition.

Get a real breakdown — free One photo, graded S to E. No card.

Questions

What is BMI?

BMI (Body Mass Index) is your weight divided by your height squared. It's a quick, population-level screening number used by health organizations, but it doesn't distinguish between muscle and fat — it only knows total weight.

Is BMI accurate for muscular people?

No. BMI can't tell the difference between muscle and fat, so a heavily muscled, lean person can score as "overweight" or "obese" on BMI despite having very little body fat. It was designed as a population-level statistical tool, not an individual body-composition measurement.

What is a normal BMI range?

The WHO adult reference ranges classify under 18.5 as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight, and 30 or higher as obesity. They are screening categories, not individual health verdicts.

What should I use instead of BMI if I lift weights?

FFMI uses estimated fat-free mass rather than total body weight, but fat-free mass includes more than skeletal muscle and depends on a body-fat estimate. It can help answer a different question from BMI; neither measures physique or health on its own. A photo-based grade is a visual estimate, not a body-composition measurement.

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