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🫀 BMI & Body Composition Calculator

Calculate Body Mass Index from height and weight, see where it falls on the underweight-to-obese gauge, and get an approximate body-fat percentage and healthy-weight range.

Medicine & Biophysics3DEasy60 FPS

The BMI Formula

Body Mass Index = weight (kg) ÷ height (m)². It is a quick, population-level screening tool developed in the 19th century and popularised for public-health surveys, not an individual diagnostic measure. The four standard bands are underweight (<18.5), normal (18.5–24.9), overweight (25–29.9) and obese (≥30).

Estimating Body Fat %

This simulation uses a simplified BMI-based estimator: body fat % ≈ 1.20 × BMI + 0.23 × age − 10.8 × (1 if male, 0 if female) − 5.4. It is a rough approximation derived from population averages, not a diagnostic measurement — proper body-composition assessment uses DEXA scans, bioelectrical impedance or skinfold calipers, since BMI alone cannot distinguish muscle mass from fat mass.

Why BMI Has Limits

BMI does not know whether your mass is muscle, bone or fat, so very muscular people can be classified "overweight" despite low body fat, and it says nothing about where fat is distributed — visceral fat around the organs carries more health risk than subcutaneous fat under the skin, at the same BMI. Waist circumference and body-fat percentage are often better indicators of metabolic risk.

About this simulation

This simulation turns Body Mass Index into a visual gauge: drag height, weight, age and sex and watch a marker slide across four coloured zones — underweight, normal, overweight and obese — while a simplified formula also estimates body-fat percentage and the healthy-weight range for your height. It is designed for quick, intuitive screening, not medical diagnosis.

🔬 What it shows

A horizontal gauge divided into the four standard BMI bands, each shown as a coloured zone from underweight (blue) through normal (green) and overweight (amber) to obese (red), with a pulsing white marker positioned exactly at your computed BMI value.

🎮 How to use

Drag Height and Weight to compute BMI = weight ÷ height², adjust Age and toggle Sex to refine the body-fat percentage estimate, and read off the healthy-weight range (in kg) for your height directly beneath the gauge.

💡 Did you know?

Two people can share an identical BMI and yet have very different body compositions — a muscular athlete and a sedentary person of the same height and weight can land on the exact same point on this gauge, which is precisely why BMI is a screening tool rather than a diagnosis.

Frequently asked questions

How is BMI calculated?

BMI = weight in kilograms divided by height in metres squared. It was designed as a simple, population-level screening measure, using only height and weight, so it is fast to compute but blind to how that mass is distributed between muscle, bone and fat.

How accurate is the body-fat percentage estimate?

The formula used here, body fat % ≈ 1.20 × BMI + 0.23 × age − 10.8 × (male) − 5.4, is a widely cited approximation derived from population data, not a direct measurement. It can be off by several percentage points for any individual, especially very muscular or very lean people. Accurate body-fat measurement needs a DEXA scan, hydrostatic weighing or bioelectrical impedance analysis.

What counts as a healthy weight range?

This simulation defines it as the weight range that keeps BMI between 18.5 and 24.9 for your entered height — the conventional "normal" band. It is a general guideline; genetics, ethnicity, muscle mass, age and overall health context all affect what weight is actually healthy for a given individual.

Why can BMI be misleading for muscular people?

Muscle is denser than fat, so a heavily muscled person can have a high BMI while carrying very little body fat. Because BMI only uses height and weight, it cannot tell the difference between a kilogram of muscle and a kilogram of fat — it just adds up total mass.

Is this simulation medical advice?

No. It is an educational approximation intended to illustrate how BMI and body-fat estimates are calculated. It is not a diagnostic tool, and anyone with concerns about their weight, body composition or health should consult a qualified healthcare professional.

⚙ Under the hood

Calculate Body Mass Index from height and weight, see where it falls on the underweight-to-obese gauge, and get an approximate body-fat percentage and healthy-weight range.

Three.jsBMIbody compositionbody fat percentagehealth

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install