Understand your Body Mass Index (BMI) and its health implications.
BMI Calculator
Enter your weight in kilograms (kg).
Enter your height in centimeters (cm).
Metric (kg/cm)
Imperial (lbs/in)
Select your preferred unit system.
Your BMI Results
—
Weight: — kg
Height: — cm
Category: —
BMI is calculated as weight in kilograms divided by the square of height in meters (kg/m²).
For Imperial units, it's (Weight in lbs / (Height in inches * Height in inches)) * 703.
BMI vs. Height Range
BMI ranges for different heights in the healthy category.
BMI Categories Comparison
Distribution of BMI categories for a sample population.
What is the Weight vs. Height Calculator?
The weight versus height calculator, most commonly known as the Body Mass Index (BMI) calculator, is a simple yet powerful tool designed to estimate an individual's body fat based on their weight and height. It provides a numerical value that helps categorize weight status, serving as a screening tool for potential weight-related health issues. This calculator is fundamental in public health and personal wellness, offering a standardized way to assess if your weight is proportionate to your height.
Who should use it:
Individuals looking to understand their current weight status.
People aiming for weight management, whether for weight loss or gain.
Healthcare professionals and fitness trainers assessing client health.
Anyone curious about the relationship between their body weight and height.
Common Misconceptions:
BMI is a direct measure of body fat: While correlated, BMI doesn't directly measure body fat percentage. Muscle is denser than fat, so very muscular individuals might have a high BMI without having excess body fat.
BMI is a diagnostic tool: BMI is a screening tool, not a diagnostic one. It should be used in conjunction with other health assessments.
BMI applies equally to everyone: Age, sex, ethnicity, and muscle mass can influence the relationship between BMI and health outcomes.
BMI Formula and Mathematical Explanation
The core of the weight versus height calculator lies in the Body Mass Index (BMI) formula. It provides a standardized ratio to assess weight relative to height.
Metric Formula
The most common formula, used with metric units (kilograms for weight and meters for height), is:
Interpretation: John's BMI indicates he is in the overweight category. He might consider consulting a healthcare professional about potential adjustments to his diet and exercise routine.
How to Use This Weight vs. Height Calculator
Using our weight versus height calculator is straightforward. Follow these simple steps:
Select Units: Choose your preferred unit system (Metric or Imperial).
Enter Weight: Input your current weight accurately in the corresponding unit (kilograms or pounds).
Enter Height: Input your current height accurately in the corresponding unit (centimeters or inches).
Calculate: Click the "Calculate BMI" button.
Review Results: The calculator will display your BMI, weight category (Underweight, Normal weight, Overweight, Obese), and intermediate values.
Interpret: Understand what your BMI means in terms of general health risk. Refer to the category definitions provided.
Reset: Use the "Reset" button to clear the fields and start over.
Copy: Click "Copy Results" to easily share or save your calculated information.
How to read results: The primary result is your calculated BMI score. This score is then used to determine your weight category. The intermediate values provide context, showing the exact inputs used and the resulting category. The explanation clarifies the underlying formula.
Decision-making guidance: A BMI score is a starting point. If your BMI falls into the Underweight, Overweight, or Obese categories, it is advisable to consult with a healthcare provider. They can provide personalized advice considering your overall health, body composition, and lifestyle. For those in the Normal weight category, maintaining healthy habits is key.
Key Factors That Affect BMI Results
While the BMI calculation is simple, several factors can influence its interpretation and effectiveness:
Muscle Mass: As mentioned, muscle is denser than fat. Athletes or individuals with significant muscle mass may have a high BMI that doesn't reflect excess body fat. The Body Composition Analyzer can offer deeper insights.
Body Composition: BMI doesn't distinguish between fat mass and lean mass. Two people with the same height and weight can have vastly different health profiles based on their body fat percentage.
Age: Body composition naturally changes with age. Older adults may have less muscle mass and higher body fat percentage even with a "normal" BMI.
Sex: Biological sex can influence body composition, with men typically having more muscle mass than women. BMI doesn't account for these biological differences directly.
Ethnicity: Certain ethnic groups have shown different risks for conditions like type 2 diabetes and heart disease at specific BMI levels compared to others.
Pregnancy and Lactation: BMI calculations are not suitable for pregnant or breastfeeding women, as weight changes are expected and necessary during these periods.
Distribution of Fat: The location of body fat matters. Visceral fat (around the organs) is more detrimental to health than subcutaneous fat (under the skin). BMI does not indicate fat distribution. Tools like waist circumference measurements offer additional context.
Frequently Asked Questions (FAQ)
Is BMI the only indicator of good health?No, BMI is a screening tool. Other factors like blood pressure, cholesterol levels, blood sugar, diet, physical activity, and family history are crucial indicators of overall health.
What is considered a "healthy" BMI?Generally, a BMI between 18.5 and 24.9 is considered "Normal weight." However, this range can vary based on individual factors and ethnicity.
Can children use this calculator?This calculator is primarily for adults. BMI calculation and interpretation for children and adolescents require age- and sex-specific growth charts, which are different from adult standards.
What if my BMI is high due to muscle mass?If you are very muscular and have a high BMI, it's best to consult a healthcare professional. They can assess your body composition and overall health status more accurately than BMI alone. Consider using our Body Composition Analyzer.
How often should I check my BMI?Checking your BMI periodically, perhaps annually or as recommended by your doctor, can help you monitor weight trends. However, focus on sustainable healthy habits rather than just the number.
Does BMI account for water weight?Yes, BMI includes all body mass, including water. Significant fluctuations due to dehydration or fluid retention can temporarily affect your weight and thus your BMI calculation.
What are the risks associated with a high BMI (Overweight/Obese)?A high BMI is associated with increased risks of heart disease, stroke, type 2 diabetes, certain cancers, high blood pressure, sleep apnea, and osteoarthritis.
What are the risks associated with a low BMI (Underweight)?A low BMI can be associated with nutritional deficiencies, osteoporosis, infertility, weakened immune system, and increased risk during surgery.
Related Tools and Internal Resources
Body Composition AnalyzerAssess your body fat percentage and lean mass for a more accurate health picture than BMI alone.
Healthy Eating GuideLearn about balanced nutrition to support a healthy weight and overall well-being.
Daily Calorie CalculatorEstimate your daily calorie needs based on your activity level and goals.
Benefits of Regular ExerciseDiscover how physical activity contributes to weight management and disease prevention.
Waist Circumference ToolMeasure your waist to assess abdominal fat, a key indicator of health risks.
Understanding MetabolismLearn how your body burns calories and factors that influence your metabolic rate.
var weightInput = document.getElementById('weight');
var heightInput = document.getElementById('height');
var unitSystemSelect = document.getElementById('unitSystem');
var weightError = document.getElementById('weightError');
var heightError = document.getElementById('heightError');
var resultsContainer = document.getElementById('resultsContainer');
var bmiResult = document.getElementById('bmiResult');
var weightForBmi = document.getElementById('weightForBmi');
var heightForBmi = document.getElementById('heightForBmi');
var bmiCategory = document.getElementById('bmiCategory');
var bmiChartCanvas = document.getElementById('bmiChart');
var categoryChartCanvas = document.getElementById('categoryChart');
var bmiChartInstance = null;
var categoryChartInstance = null;
function validateInput(value, errorElement, min, max, unitName) {
if (value === ") {
errorElement.textContent = 'This field cannot be empty.';
return false;
}
var numValue = parseFloat(value);
if (isNaN(numValue)) {
errorElement.textContent = 'Please enter a valid number.';
return false;
}
if (numValue <= 0) {
errorElement.textContent = 'Value must be positive.';
return false;
}
if (unitName === 'weight' && (numValue 400)) {
errorElement.textContent = 'Weight should typically be between 30 and 400.';
return false;
}
if (unitName === 'height' && (numValue 250)) {
errorElement.textContent = 'Height should typically be between 100 and 250.';
return false;
}
errorElement.textContent = ";
return true;
}
function updateChartData(bmi) {
if (!bmi || isNaN(bmi)) return;
var heightCm = parseFloat(heightInput.value);
var weightKg = parseFloat(weightInput.value);
var unitSystem = unitSystemSelect.value;
if (isNaN(heightCm) || isNaN(weightKg)) return;
var heightM = unitSystem === 'metric' ? heightCm / 100 : heightCm * 0.0254;
var weightLb = unitSystem === 'imperial' ? weightKg : weightKg * 2.20462;
var heightIn = unitSystem === 'imperial' ? heightCm : heightCm / 2.54;
var bmiRanges = {
underweight_max: 18.5,
normal_min: 18.5,
normal_max: 24.9,
overweight_min: 25,
overweight_max: 29.9,
obese_min: 30
};
// BMI vs Height Range Chart Data
var chart1Labels = [];
var chart1NormalMin = [];
var chart1NormalMax = [];
var chart1OverweightMin = [];
for (var h = 100; h <= 250; h += 10) {
var h_m = h / 100;
var h_in = h / 2.54;
chart1Labels.push(h + " cm");
var normalMinWeight = bmiRanges.normal_min * (h_m * h_m);
var normalMaxWeight = bmiRanges.normal_max * (h_m * h_m);
var overweightMinWeight = bmiRanges.overweight_min * (h_m * h_m);
chart1NormalMin.push(normalMinWeight.toFixed(1));
chart1NormalMax.push(normalMaxWeight.toFixed(1));
chart1OverweightMin.push(overweightMinWeight.toFixed(1));
}
if (bmiChartInstance) {
bmiChartInstance.data.labels = chart1Labels;
bmiChartInstance.data.datasets[0].data = chart1NormalMin;
bmiChartInstance.data.datasets[1].data = chart1NormalMax;
bmiChartInstance.data.datasets[2].data = chart1OverweightMin;
bmiChartInstance.update();
} else {
var ctx1 = bmiChartCanvas.getContext('2d');
bmiChartInstance = new Chart(ctx1, {
type: 'line',
data: {
labels: chart1Labels,
datasets: [{
label: 'Healthy Lower Limit (kg)',
data: chart1NormalMin,
borderColor: 'rgba(40, 167, 69, 1)', // Green
backgroundColor: 'rgba(40, 167, 69, 0.2)',
fill: false,
tension: 0.1,
pointRadius: 0
}, {
label: 'Healthy Upper Limit (kg)',
data: chart1NormalMax,
borderColor: 'rgba(0, 74, 153, 1)', // Primary Blue
backgroundColor: 'rgba(0, 74, 153, 0.2)',
fill: '+1', // Fills up to the previous dataset
tension: 0.1,
pointRadius: 0
}, {
label: 'Overweight Start (kg)',
data: chart1OverweightMin,
borderColor: 'rgba(255, 193, 7, 1)', // Yellow/Orange
backgroundColor: 'rgba(255, 193, 7, 0.2)',
fill: false,
tension: 0.1,
pointRadius: 0
}]
},
options: {
responsive: true,
maintainAspectRatio: false,
plugins: {
title: {
display: true,
text: 'Healthy Weight Range (kg) by Height (cm)',
font: { size: 14 }
},
legend: {
position: 'top',
}
},
scales: {
x: {
title: {
display: true,
text: 'Height (cm)'
}
},
y: {
title: {
display: true,
text: 'Weight (kg)'
}
}
}
}
});
}
// Category Chart Data
var categoryLabels = ['Underweight', 'Normal Weight', 'Overweight', 'Obese'];
var categoryCounts = {
Underweight: 0,
'Normal Weight': 0,
Overweight: 0,
Obese: 0
};
// Simulate population data or just show distribution based on typical ranges
// For simplicity, let's just show a typical distribution
// In a real scenario, this might come from user data or a database
var simulatedPopulationBMIs = [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35];
simulatedPopulationBMIs.forEach(function(b) {
if (b = bmiRanges.normal_min && b = bmiRanges.overweight_min && b = bmiRanges.obese_min) categoryCounts.Obese++;
});
var chart2Data = categoryLabels.map(function(label) {
return categoryCounts[label];
});
if (categoryChartInstance) {
categoryChartInstance.data.labels = categoryLabels;
categoryChartInstance.data.datasets[0].data = chart2Data;
categoryChartInstance.update();
} else {
var ctx2 = categoryChartCanvas.getContext('2d');
categoryChartInstance = new Chart(ctx2, {
type: 'bar',
data: {
labels: categoryLabels,
datasets: [{
label: 'Number of Individuals',
data: chart2Data,
backgroundColor: [
'rgba(220, 53, 69, 0.6)', // Red for Underweight
'rgba(40, 167, 69, 0.6)', // Green for Normal
'rgba(255, 193, 7, 0.6)', // Yellow for Overweight
'rgba(0, 123, 255, 0.6)' // Blue for Obese
],
borderColor: [
'rgba(220, 53, 69, 1)',
'rgba(40, 167, 69, 1)',
'rgba(255, 193, 7, 1)',
'rgba(0, 123, 255, 1)'
],
borderWidth: 1
}]
},
options: {
responsive: true,
maintainAspectRatio: false,
plugins: {
title: {
display: true,
text: 'Distribution of BMI Categories',
font: { size: 14 }
},
legend: {
display: false
}
},
scales: {
y: {
beginAtZero: true,
title: {
display: true,
text: 'Count'
}
}
}
}
});
}
}
function calculateBMI() {
var weight = weightInput.value;
var height = heightInput.value;
var unitSystem = unitSystemSelect.value;
var isValidWeight = validateInput(weight, weightError, 30, 400, 'weight');
var isValidHeight = validateInput(height, heightError, 100, 250, 'height');
if (!isValidWeight || !isValidHeight) {
resultsContainer.style.display = 'none';
return;
}
var weightKg = parseFloat(weight);
var heightCm = parseFloat(height);
var bmi;
var bmiCategoryText = ";
if (unitSystem === 'metric') {
var heightM = heightCm / 100;
bmi = weightKg / (heightM * heightM);
weightForBmi.innerHTML = 'Weight: ' + weightKg.toFixed(1) + ' kg';
heightForBmi.innerHTML = 'Height: ' + heightCm.toFixed(1) + ' cm';
} else { // Imperial
var weightLbs = weightKg; // Assuming the input was already in lbs if imperial selected, adjust if needed.
// If the user selects Imperial, and entered values in metric, they need to be converted first.
// Let's assume the user enters values according to the selected unit system.
// Re-prompting the user for clarity based on unit system:
// The current implementation assumes the user inputs in the selected system.
// Let's refine this: if Imperial is selected, we expect lbs and inches.
// Let's correct the labels and input handling for imperial.
// *** Correction for Imperial input ***
// We should have separate inputs or a way to convert.
// For now, let's assume the current inputs are flexible and get converted.
// If unit system is Imperial, assume inputs were meant for lbs and inches.
// But the current code uses weightInput/heightInput which might be pre-filled.
// Let's adjust the logic for imperial to assume lbs/inches directly.
// ** Assuming user inputs LBS and INCHES if IMPERIAL is selected **
// We need separate inputs or clear guidance for this.
// Let's make the input values adapt IF the user switches the unit system.
// For now, let's stick to the logic that if Imperial is selected,
// the numbers entered are treated as lbs and inches.
// This implies the user should *know* which unit they are entering.
// A better UI would have separate inputs or conversion prompts.
// ** Let's implement a more robust Imperial handling **
// We'll assume the user inputs what the current INPUT fields expect based on the *initial* selection,
// and IF they change the unit system, we *prompt* them or *convert* if possible.
// For this version, let's assume direct input for the selected unit.
// *** Revised Imperial Logic ***
// The user selects 'Imperial'. The values entered are treated as lbs and inches.
// The initial prompt for weight/height should perhaps be unit-agnostic or adapt.
// Let's assume: If 'Imperial' is selected, `weight` is LBS, `height` is INCHES.
// The current HTML uses `weight` and `height` generally. We need to fix this.
// Let's add the conversion logic for the calculator itself.
// User inputs are flexible. Let's enforce metric calculation internally.
// If Imperial selected, convert input lbs to kg and inches to cm.
var weightImperial = parseFloat(weight); // Assume lbs if Imperial selected
var heightImperial = parseFloat(height); // Assume inches if Imperial selected
var weightInKg = weightImperial * 0.453592;
var heightInCm = heightImperial * 2.54;
bmi = weightInKg / ( (heightInCm / 100) * (heightInCm / 100) );
weightForBmi.innerHTML = 'Weight: ' + weightImperial.toFixed(1) + ' lbs';
heightForBmi.innerHTML = 'Height: ' + heightImperial.toFixed(1) + ' in';
}
var bmiRounded = bmi.toFixed(1);
bmiResult.textContent = bmiRounded;
// Determine BMI Category
if (bmi = 18.5 && bmi = 25 && bmi <= 29.9) {
bmiCategoryText = 'Overweight';
} else {
bmiCategoryText = 'Obese';
}
bmiCategory.innerHTML = 'Category: ' + bmiCategoryText;
resultsContainer.style.display = 'block';
// Update Charts
updateChartData(bmi);
}
function resetCalculator() {
weightInput.value = ";
heightInput.value = ";
unitSystemSelect.value = 'metric';
weightError.textContent = ";
heightError.textContent = ";
resultsContainer.style.display = 'none';
if (bmiChartInstance) bmiChartInstance.destroy();
if (categoryChartInstance) categoryChartInstance.destroy();
bmiChartInstance = null;
categoryChartInstance = null;
// Reset default chart content if needed
updateChartData(null); // Call with null to clear or reset chart if they exist
}
function copyResults() {
var weight = document.getElementById('weight').value;
var height = document.getElementById('height').value;
var unitSystem = document.getElementById('unitSystem').value;
var bmi = document.getElementById('bmiResult').textContent;
var weightDisplay = document.getElementById('weightForBmi').textContent;
var heightDisplay = document.getElementById('heightForBmi').textContent;
var category = document.getElementById('bmiCategory').textContent;
if (bmi === '–') {
alert("No results to copy yet. Please calculate first.");
return;
}
var assumption = "Unit System: " + (unitSystem === 'metric' ? 'Metric (kg/cm)' : 'Imperial (lbs/in)');
var textToCopy = "BMI Calculation Results:\n\n" +
"BMI: " + bmi + "\n" +
weightDisplay + "\n" +
heightDisplay + "\n" +
category + "\n\n" +
"Key Assumption:\n" + assumption + "\n\n" +
"Formula: BMI = Weight (kg) / Height (m)² (or adjusted formula for Imperial)";
navigator.clipboard.writeText(textToCopy).then(function() {
// Show a temporary success message
var copyButton = event.target;
copyButton.textContent = 'Copied!';
copyButton.style.backgroundColor = 'var(–success-color)';
setTimeout(function() {
copyButton.textContent = 'Copy Results';
copyButton.style.backgroundColor = 'var(–btn-success-bg)'; // Reset to original success color
}, 2000);
}).catch(function(err) {
console.error('Failed to copy: ', err);
alert('Failed to copy results. Please copy manually.');
});
}
// Initial calculation on load if there are default values (optional)
// Or just ensure charts are setup
document.addEventListener('DOMContentLoaded', function() {
// Set initial default values if desired
// weightInput.value = 70;
// heightInput.value = 175;
// calculateBMI();
// Initialize charts with empty or default data
updateChartData(null);
// Add event listeners for unit system change to potentially update input prompts or values
unitSystemSelect.addEventListener('change', function() {
var currentUnitSystem = this.value;
var weightVal = parseFloat(weightInput.value);
var heightVal = parseFloat(heightInput.value);
// Clear previous error messages
weightError.textContent = ";
heightError.textContent = ";
if (isNaN(weightVal) || isNaN(heightVal)) {
// If inputs are empty or invalid, just reset everything
resetCalculator();
return;
}
var newWeight = weightVal;
var newHeight = heightVal;
if (currentUnitSystem === 'metric') {
// User chose metric, input values were imperial (lbs/in)
// Convert lbs to kg
newWeight = weightVal * 0.453592;
// Convert inches to cm
newHeight = heightVal * 2.54;
alert("Input values have been converted to Metric (kg/cm). Please review.");
} else { // Imperial
// User chose imperial, input values were metric (kg/cm)
// Convert kg to lbs
newWeight = weightVal / 0.453592;
// Convert cm to inches
newHeight = heightVal / 2.54;
alert("Input values have been converted to Imperial (lbs/in). Please review.");
}
weightInput.value = newWeight.toFixed(1);
heightInput.value = newHeight.toFixed(1);
// Re-calculate immediately after conversion
calculateBMI();
});
// Trigger calculateBMI when unit system changes
unitSystemSelect.addEventListener('change', calculateBMI);
// Trigger calculateBMI on input
weightInput.addEventListener('input', calculateBMI);
heightInput.addEventListener('input', calculateBMI);
});