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Body Mass Index (BMI) Calculator

Calculate your Body Mass Index (BMI) quickly, easily, and for free

Calculator: BMI

Result

Enter the values and click the button to view the result

Result based on the provided information

Related Features

BMI
BMI (Youth)
BMR + TDEE
Calories by Goal & Macros
Ideal Weight & Body Fat Percentage

BMI Calculator – Online, Fast & Free

Want to quickly and reliably determine your Body Mass Index (BMI)?

Fastools offers a free online BMI calculator that provides instant results, detailed interpretation, and health tips—directly in your browser, with no registration or downloads required.

Simply enter your weight and height, click 'Calculate', and instantly receive your result with clear explanations of your BMI classification.

Our BMI tool assists students, health professionals, and anyone interested in monitoring body weight, providing reliable and easy-to-understand information.

How to use the BMI calculator?

  • 1️⃣ Enter your weight in kilograms.
  • 2️⃣ Enter your height in meters.
  • 3️⃣ Click ‘Calculate’ to see the result instantly.
  • 4️⃣ Review your BMI interpretation and health tips.

Why use the Fastools calculator?

  • ✅ Completely free and online
  • ✅ Fast and accurate results
  • ✅ Detailed interpretation to understand your BMI
  • ✅ Ideal for students, healthcare professionals, and the curious
  • ✅ Works directly in your browser—no downloads or sign-up required

Benefits of using our BMI calculator

  • 📊 Assess your weight relative to height, simply and reliably
  • ⚡ Save time with instant calculations
  • 🎯 Avoid common manual calculation errors
  • 💻 Access from any device: computer, tablet, or smartphone

Can I use the calculator to monitor my health?

Yes! The tool is perfect for those who want to monitor their weight, maintain healthy habits, and track their Body Mass Index regularly.

Start calculating your BMI online, for free and reliably, with Fastools today!

What is BMI (Body Mass Index)?

BMI, or Body Mass Index, is a measure used to assess the relationship between a person’s weight and height. This indicator helps identify whether an individual is underweight, at a healthy weight, overweight, or obese.

Based on simple mathematical calculations, BMI is widely used by health professionals, medical institutions, and international bodies such as the World Health Organization (WHO) as an initial tool for assessing nutritional status.

It is important to note that BMI does not directly measure body fat, but provides a general estimate of the risk associated with body weight relative to height. Therefore, it should be interpreted alongside other clinical tests and assessments.

BMI is primarily intended for adults and is widely used in routine medical check-ups, epidemiological studies, and prevention programs for diseases related to excess or insufficient weight.

How BMI is calculated

BMI (Body Mass Index) is a widely used indicator to assess whether a person falls within the healthy weight range for their height. BMI calculation is straightforward and internationally recognized by health authorities such as the World Health Organization (WHO).

BMI formula:

$$\text{IMC} = \frac{\text{peso}}{\text{altura}^2}$$

Understand the variables in the formula:

Variable Unit Symbol
BMI Kilograms per square meter kg/m2
Weight Kilograms kg
Height Meters m

BMI classification table for adults

The BMI classification table allows for quick identification of whether a person is underweight, normal weight, overweight, or obese. These values serve as clinical and epidemiological reference points for adults.

# Classification BMI (kg/m²) Description
1 Underweight Less than 18.5 Body weight below the recommended range for height, with increased risk of nutritional deficiencies and other health problems.
2 Normal weight 18.5 to 24.9 Range considered healthy, associated with lower risk of weight-related diseases.
3 Overweight 25.0–29.9 Excess body weight that may increase the risk of metabolic and cardiovascular diseases.
4 Obesity Class I 30.0–34.9 Mild obesity, associated with higher risk of type 2 diabetes, hypertension, and dyslipidemia.
5 Obesity Class II 35.0–39.9 Moderate obesity, with high risk of chronic complications and reduced quality of life.
6 Obesity Class III 40.0 or higher Severe or morbid obesity, associated with high risk of mortality and severe diseases.

Decimal values are assigned to the immediately lower range. For example, a BMI of 24.95 is still classified as normal weight, since overweight begins at 25.0 and above.

Interesting facts and important information about BMI

📜 Origin and history of BMI

  • The Body Mass Index was developed in 1832 by Adolphe Quetelet, a Belgian mathematician and astronomer.
  • Initially, BMI was developed for population-level statistical studies, not for individual diagnosis.
  • In 1995, the WHO adopted BMI as the international standard for nutritional assessment.

⚙️ How BMI is used today

  • Widely used in medical consultations, occupational exams, and health assessments.
  • Assists in early identification of risks such as diabetes, hypertension, and heart disease.
  • Essential for public health policies and epidemiological studies.

🚫 Limitations of the Body Mass Index

  • BMI does not distinguish between muscle mass and body fat.
  • It may not accurately reflect risk in individuals with abdominal fat accumulation.
  • Less accurate for athletes, older adults, and children.

🧪 BMI-complementary measurements

  • Small variations in height can significantly impact the BMI result.
  • Indicators such as the waist-to-hip ratio (WHR) help assess fat distribution.
  • Tests such as bioimpedance and DEXA provide more detailed body composition analysis.

✨ Additional BMI facts

  • Studies associate BMI values outside the ideal range with reduced life expectancy.
  • A person may have a normal BMI yet exhibit metabolic abnormalities, a phenomenon known as “normal-weight obesity” or “skinny fat”.
  • BMI should be interpreted alongside other health factors.