Body Mass Index (BMI) is a measurement of a person's leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height.
The BMI Calculation Formula
The standard calculation for BMI uses the metric system. The formula is:
BMI = weight (kg) / [height (m)]²
Standard BMI Categories
BMI Range
Category
Less than 18.5
Underweight
18.5 – 24.9
Healthy Weight
25.0 – 29.9
Overweight
30.0 or Higher
Obesity
Example Calculations
Example 1: An adult weighing 70kg with a height of 175cm (1.75m). 70 / (1.75 * 1.75) = 22.86 BMI (Healthy Weight).
Example 2: An adult weighing 95kg with a height of 180cm (1.8m). 95 / (1.8 * 1.8) = 29.32 BMI (Overweight).
Example 3: An adult weighing 50kg with a height of 165cm (1.65m). 50 / (1.65 * 1.65) = 18.37 BMI (Underweight).
Important Considerations
While BMI is a useful tool, it has limitations. It does not directly measure body fat and does not account for muscle mass, bone density, or overall body composition. Athletes or individuals with high muscle mass may have a high BMI but low body fat levels. Conversely, older adults may have a normal BMI but higher body fat.
function calculateBMI() {
var weight = document.getElementById("weightInput").value;
var heightCm = document.getElementById("heightInput").value;
var resultWrapper = document.getElementById("bmiResultWrapper");
var bmiDisplay = document.getElementById("bmiDisplay");
var categoryDisplay = document.getElementById("categoryDisplay");
var feedbackText = document.getElementById("feedbackText");
if (weight > 0 && heightCm > 0) {
var heightM = heightCm / 100;
var bmi = weight / (heightM * heightM);
var roundedBMI = bmi.toFixed(1);
resultWrapper.style.display = "block";
bmiDisplay.innerText = roundedBMI;
var category = "";
var color = "";
var feedback = "";
if (bmi = 18.5 && bmi = 25 && bmi <= 29.9) {
category = "Overweight";
color = "#f39c12";
feedback = "Your BMI indicates you are in the overweight range. Small changes in diet and regular physical activity can help manage your weight.";
} else {
category = "Obesity";
color = "#e74c3c";
feedback = "Your BMI is in the obesity range. This may increase the risk of health issues like heart disease and diabetes. Consider speaking with a doctor for a personalized health plan.";
}
categoryDisplay.innerText = category;
categoryDisplay.style.color = color;
feedbackText.innerText = feedback;
resultWrapper.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
} else {
alert("Please enter valid positive numbers for both weight and height.");
}
}