BMI Calculator
This professional BMI calculator helps adults estimate body fatness using height and weight, in either metric or US units. It instantly provides your BMI value, WHO category, BMI Prime, and your healthy weight range for your height.
Interactive BMI Calculator
This tool is intended for adults. It does not provide medical advice.
Results
Enter your details to see your BMI.
Data Source and Methodology
Primary classification reference: World Health Organization (WHO). Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894, 2000; and WHO BMI classification (Adults), updated guidance. WHO BMI Classification. Formula reference for US customary conversion: CDC Adult BMI Calculator.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Metric: \( \mathrm{BMI} = \dfrac{w_{kg}}{(h_{m})^{2}} \)
US Customary: \( \mathrm{BMI} = 703 \times \dfrac{w_{lb}}{(h_{in})^{2}} \)
BMI Prime: \( \mathrm{BMI}' = \dfrac{\mathrm{BMI}}{25} \)
Healthy weight range for a given height (m): \( w_{healthy} \in [18.5,\,24.9] \times h_{m}^{2} \)
LaTeX notation is shown; formulas are standard and unit-sensitive.
Glossary of Variables
Height (cm or ft/in): Your standing height without shoes.
Weight (kg or lb): Your body weight on a calibrated scale.
BMI: Body Mass Index computed from height and weight.
Category (WHO): Underweight, Normal, Overweight, or Obesity (Class I–III).
BMI Prime: Ratio of your BMI to 25 (upper bound of normal).
Healthy weight range: Weight interval corresponding to BMI 18.5–24.9 for your height.
How It Works: A Step-by-Step Example
Scenario: Height = 175 cm (1.75 m), Weight = 72 kg.
- Convert height to meters: 175 cm = 1.75 m.
- Apply the metric formula: \( \mathrm{BMI} = \dfrac{72}{(1.75)^2} = \dfrac{72}{3.0625} \approx 23.5 \).
- Determine category (WHO): 23.5 is in the 18.5–24.9 range → Normal.
- BMI Prime: \( 23.5 / 25 = 0.94 \).
- Healthy weight range at 1.75 m: \( [18.5,24.9] \times (1.75)^2 = [56.6, 76.2] \) kg (rounded).
Frequently Asked Questions (FAQ)
Is BMI a diagnostic tool?
No. BMI is a screening measure. A healthcare professional should consider other factors (waist circumference, body composition, health history).
What are the adult BMI categories?
WHO: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obesity I 30–34.9, Obesity II 35–39.9, Obesity III ≥40.
Should older adults interpret BMI differently?
Aging changes body composition; clinical interpretation may differ. Discuss with a healthcare provider.
How precise should my inputs be?
One decimal place is usually sufficient. The calculator accepts decimals for higher precision.
Can clothing or time of day affect results?
Yes. Measure height without shoes and weight with minimal clothing, preferably at the same time of day.
Does the tool support both unit systems?
Yes. Toggle between Metric (cm, kg) and US (ft/in, lb). Formulas adjust automatically.
Where can I find BMI-for-age charts for children?
See CDC growth charts and BMI-for-age percentiles for children and teens: CDC Growth Charts.