BMI & Body Fat Calculator
:root {
–primary-blue: #004a99;
–success-green: #28a745;
–light-background: #f8f9fa;
–dark-text: #333;
–border-color: #ddd;
}
body {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background-color: var(–light-background);
color: var(–dark-text);
line-height: 1.6;
margin: 0;
padding: 20px;
display: flex;
flex-direction: column;
align-items: center;
}
.calculator-container {
background-color: #ffffff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
max-width: 700px;
width: 100%;
margin-bottom: 30px;
}
h1, h2 {
color: var(–primary-blue);
text-align: center;
margin-bottom: 20px;
}
.input-group {
margin-bottom: 15px;
display: flex;
align-items: center;
flex-wrap: wrap;
}
.input-group label {
flex: 1;
min-width: 120px;
margin-right: 10px;
font-weight: bold;
color: var(–dark-text);
text-align: right;
}
.input-group input[type="number"],
.input-group select {
flex: 2;
padding: 10px 12px;
border: 1px solid var(–border-color);
border-radius: 4px;
box-sizing: border-box;
font-size: 1em;
min-width: 150px;
}
.input-group input[type="number"]:focus,
.input-group select:focus {
outline: none;
border-color: var(–primary-blue);
box-shadow: 0 0 0 2px rgba(0, 74, 153, 0.2);
}
.button-group {
text-align: center;
margin-top: 25px;
}
button {
background-color: var(–primary-blue);
color: white;
border: none;
padding: 12px 25px;
border-radius: 5px;
font-size: 1.1em;
cursor: pointer;
transition: background-color 0.3s ease, transform 0.2s ease;
}
button:hover {
background-color: #003b7f;
transform: translateY(-2px);
}
.result-container {
background-color: var(–primary-blue);
color: white;
padding: 25px;
border-radius: 8px;
margin-top: 30px;
text-align: center;
box-shadow: 0 4px 15px rgba(0, 74, 153, 0.3);
}
.result-container h3 {
margin-top: 0;
color: white;
font-size: 1.5em;
}
#bmiResult, #bodyFatResult, #bmiCategory, #bfCategory {
font-size: 2.2em;
font-weight: bold;
margin-bottom: 10px;
display: block; /* Ensures it takes full width for spacing */
}
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text-align: center;
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/* Responsive adjustments */
@media (max-width: 600px) {
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flex-direction: column;
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text-align: center;
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margin-bottom: 5px;
text-align: center;
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.input-group input[type="number"],
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button {
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padding: 15px;
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}
BMI & Body Fat Calculator
Calculate your Body Mass Index (BMI) and estimate your Body Fat Percentage.
Your Health Metrics
Understanding BMI and Body Fat Percentage
Body Mass Index (BMI) and Body Fat Percentage are two key indicators used to assess an individual's health status concerning their weight. While BMI provides a general overview, Body Fat Percentage offers a more nuanced understanding of body composition.
Body Mass Index (BMI)
BMI is a measure of body weight relative to height. It's a simple screening tool, but it doesn't directly measure body fat. It categorizes individuals into underweight, normal weight, overweight, and obese.
How BMI is Calculated:
BMI = weight (kg) / [height (m)]²
Or, using Imperial units:
BMI = [weight (lb) / height (in)²] x 703
The formulas above are used to calculate BMI. For ease of use, our calculator handles the unit conversions.
BMI Categories (WHO Standard):
- Underweight: Below 18.5
- Normal weight: 18.5 – 24.9
- Overweight: 25 – 29.9
- Obese: 30 or greater
It's important to note that BMI may not be accurate for individuals with high muscle mass (like athletes) or for pregnant women and the elderly.
Body Fat Percentage
Body Fat Percentage is the proportion of your total body weight that is fat. It is considered a more direct measure of health and fitness than BMI alone, as it distinguishes between fat mass and lean mass (muscles, bones, organs).
Estimating body fat percentage often involves more complex measurements or formulas. For this calculator, we use a common formula that considers gender, age, waist circumference, and optionally hip and neck circumference, and forearm. This method provides a reasonable estimate.
Formulas Used (Example for Male):
Men: BF% = 495 / (1.0324 – 0.19077 * log10(waist – neck) + 0.15457 * log10(height)) – 450
Women: BF% = 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450
Note: Some formulas might use forearm circumference as well. The specific formula implementation here is a simplification for user accessibility and estimation. Units must be consistent (e.g., all in inches or all in cm for measurements). The calculator handles conversion.
The interpretation of body fat percentage can vary based on age and gender. Generally:
General Body Fat Percentage Guidelines:
For Men:
- Essential Fat: 2-5%
- Athletes: 6-13%
- Fitness: 14-17%
- Average: 18-24%
- Obese: 25%+
For Women:
- Essential Fat: 10-13%
- Athletes: 14-20%
- Fitness: 21-24%
- Average: 25-31%
- Obese: 32%+
These are general guidelines, and individual health should always be assessed by a healthcare professional.
Use Cases
These calculators are useful for:
- Monitoring weight and body composition changes over time.
- Assessing general health risks associated with weight.
- Setting personal fitness and health goals.
- Tracking progress during diet and exercise programs.
Always consult with a healthcare provider for personalized health advice and diagnosis.
function convertToCm(value, unit) {
if (unit === 'in') {
return value * 2.54;
} else if (unit === 'ft') {
return value * 30.48;
}
return value; // Already in cm
}
function convertToInches(value, unit) {
if (unit === 'cm') {
return value / 2.54;
} else if (unit === 'ft') {
return value * 12;
}
return value; // Already in inches
}
function convertToCmOrIn(value, unit) {
if (unit === 'in') {
return value / 2.54; // Convert inches to cm for consistent calculation
}
return value; // Already in cm
}
function calculateBMIAndBodyFat() {
var weight = parseFloat(document.getElementById("weight").value);
var weightUnit = document.getElementById("weightUnit").value;
var height = parseFloat(document.getElementById("height").value);
var heightUnit = document.getElementById("heightUnit").value;
var age = parseInt(document.getElementById("age").value);
var gender = document.getElementById("gender").value;
var waist = parseFloat(document.getElementById("waist").value);
var waistUnit = document.getElementById("waistUnit").value;
var hip = parseFloat(document.getElementById("hip").value);
var hipUnit = document.getElementById("hipUnit").value;
var neck = parseFloat(document.getElementById("neck").value);
var neckUnit = document.getElementById("neckUnit").value;
var forearm = parseFloat(document.getElementById("forearm").value);
var forearmUnit = document.getElementById("forearmUnit").value;
var resultsDiv = document.getElementById("results");
var bmiResultSpan = document.getElementById("bmiResult");
var bmiCategorySpan = document.getElementById("bmiCategory");
var bodyFatResultSpan = document.getElementById("bodyFatResult");
var bfCategorySpan = document.getElementById("bfCategory");
// — Input Validation —
if (isNaN(weight) || isNaN(height) || isNaN(age) || isNaN(waist) || isNaN(hip) || isNaN(neck)) {
alert("Please enter valid numbers for all required fields.");
return;
}
if (height <= 0 || weight <= 0 || age <= 0 || waist <= 0 || neck <= 0) {
alert("Height, weight, age, waist, and neck must be positive values.");
return;
}
if (gender === "female" && hip 0) {
bmi = weight / (heightInMeters * heightInMeters);
bmi = parseFloat(bmi.toFixed(1)); // Round to 1 decimal place
} else {
bmi = NaN;
}
var bmiCategory = "";
if (!isNaN(bmi)) {
if (bmi = 18.5 && bmi = 25 && bmi neck
if (waistForFormula > neckForFormula && heightForFormula > 0) {
var logWaistMinusNeck = Math.log10(waistForFormula – neckForFormula);
var logHeight = Math.log10(heightForFormula);
bodyFatPercentage = 495 / (1.0324 – 0.19077 * logWaistMinusNeck + 0.15457 * logHeight) – 450;
}
} else { // female
// US Navy Method for Women
// BF% = 495 / (1.29579 – 0.35004 * log10(waist + hip – neck) + 0.22100 * log10(height)) – 450
// Ensure waist + hip > neck
if ((waistForFormula + hipForFormula) > neckForFormula && heightForFormula > 0) {
var logWaistHipMinusNeck = Math.log10(waistForFormula + hipForFormula – neckForFormula);
var logHeight = Math.log10(heightForFormula);
bodyFatPercentage = 495 / (1.29579 – 0.35004 * logWaistHipMinusNeck + 0.22100 * logHeight) – 450;
}
}
bodyFatPercentage = parseFloat(bodyFatPercentage.toFixed(1)); // Round to 1 decimal place
var bfCategory = "";
if (!isNaN(bodyFatPercentage)) {
if (gender === "male") {
if (bodyFatPercentage < 2) bodyFatPercentage = 2; // Minimum essential fat
if (bodyFatPercentage < 14) bfCategory = "Athletes/Fitness";
else if (bodyFatPercentage < 18) bfCategory = "Average";
else if (bodyFatPercentage < 25) bfCategory = "Above Average";
else bfCategory = "Obese";
} else { // female
if (bodyFatPercentage < 10) bodyFatPercentage = 10; // Minimum essential fat
if (bodyFatPercentage < 21) bfCategory = "Athletes/Fitness";
else if (bodyFatPercentage < 25) bfCategory = "Average";
else if (bodyFatPercentage < 32) bfCategory = "Above Average";
else bfCategory = "Obese";
}
}
// — Display Results —
if (!isNaN(bmi)) {
bmiResultSpan.textContent = bmi;
bmiCategorySpan.textContent = "(" + bmiCategory + ")";
} else {
bmiResultSpan.textContent = "N/A";
bmiCategorySpan.textContent = "";
}
if (!isNaN(bodyFatPercentage)) {
bodyFatResultSpan.textContent = bodyFatPercentage + "%";
bfCategorySpan.textContent = "(" + bfCategory + ")";
} else {
bodyFatResultSpan.textContent = "N/A";
bfCategorySpan.textContent = "";
}
resultsDiv.style.display = "block";
}