Your essential tool for accurate Lean Body Weight calculations in anesthesia.
Lean Body Weight (LBW) Calculator
Male
Female
Select the biological sex assigned at birth for the calculation.
If unknown, leave blank or use a typical estimate (e.g., 20-30% for males, 30-40% for females).
Calculation Results
LBW vs. Total Weight Comparison
Comparison of Total Body Weight and Calculated Lean Body Weight
Typical Weight Ranges & LBW Estimates
Metric
Unit
Typical Value
Typical LBW Estimate
Illustrative comparison for different body compositions.
Understanding and Calculating Lean Body Weight for Anesthesia
What is Lean Body Weight (LBW) in Anesthesia?
{primary_keyword} refers to the weight of an individual's body minus their fat mass. This metric is crucial in anesthesiology because many anesthetic drugs are distributed and metabolized based on the body's non-fat components, such as muscle, bone, and organs. Accurately determining LBW helps anesthesiologists to:
Calculate appropriate drug dosages: Many drugs' pharmacokinetics (absorption, distribution, metabolism, excretion) are more closely related to LBW than total body weight, especially in obese or cachectic patients.
Predict drug response and duration: LBW can influence how quickly a drug takes effect, how widely it distributes, and how long it lasts in the system.
Minimize adverse effects: Overdosing due to inaccurate weight estimations can lead to prolonged recovery, respiratory depression, or cardiovascular instability.
Optimize patient safety: Precise dosing contributes significantly to patient safety during surgical procedures.
Who should use it? Anesthesiologists, surgeons, intensivists, pharmacists, and other healthcare professionals involved in patient care requiring precise drug dosing, particularly in critical care settings or for patients with significant deviations from average body composition.
Common misconceptions about LBW in anesthesia:
LBW is the same as ideal body weight (IBW): While related, IBW is a theoretical weight for a given height, whereas LBW is a calculated value based on actual body composition.
Total body weight is always sufficient for dosing: This can lead to significant dosing errors, especially in extremes of weight or body fat.
LBW is only relevant for obese patients: While most critical for obese patients, it's also important for underweight or malnourished individuals.
Lean Body Weight (LBW) Formula and Mathematical Explanation
There are several formulas to estimate Lean Body Weight (LBW). A commonly used and relatively straightforward method involves calculating Fat Mass (FM) first, then subtracting it from Total Body Weight (TBW).
Calculating Fat Mass (FM)
Fat Mass is derived from the total body weight and the percentage of body fat.
Formula:FM = TBW * (BF% / 100)
Where:
FM = Fat Mass
TBW = Total Body Weight
BF% = Body Fat Percentage
Calculating Lean Body Weight (LBW)
Once Fat Mass is determined, it's subtracted from Total Body Weight to find Lean Body Weight.
Formula:LBW = TBW - FM
Substituting the FM formula:
Combined Formula:LBW = TBW - (TBW * (BF% / 100))
This can be simplified to:
Simplified Formula:LBW = TBW * (1 - (BF% / 100))
Formulas incorporating Sex, Height, Age and Weight (e.g., James Equation):
While the above is a direct calculation from body fat percentage, anesthesiologists sometimes use predictive equations when body fat percentage is unknown. A common set of predictive equations are the James equations, which estimate LBW directly based on sex, height, weight, and age:
The vertical distance from the bottom of the feet to the top of the head.
cm
Males: 160-190 cm, Females: 150-180 cm
Age
The duration of existence since birth.
years
Adults: 18-90+ years
Key variables used in Lean Body Weight calculations.
Practical Examples (Real-World Use Cases)
Example 1: Obese Patient
A 55-year-old male patient weighs 150 kg and has an estimated body fat percentage of 45%. He requires surgery under general anesthesia.
Inputs: Sex: Male, Weight: 150 kg, Height: 180 cm, Age: 55 years, Body Fat %: 45%
Calculation (using direct method):
Fat Mass = 150 kg * (45 / 100) = 67.5 kg
LBW = 150 kg – 67.5 kg = 82.5 kg
Result: The patient's Lean Body Weight is calculated as 82.5 kg.
Interpretation: Anesthesiologists might use 82.5 kg as the basis for calculating dosages of certain drugs (e.g., propofol infusion rates, opioid boluses) rather than the full 150 kg, potentially leading to safer and more predictable anesthetic effects and faster recovery.
Example 2: Underweight Patient
A 70-year-old female patient weighs 45 kg, is 155 cm tall, and has a body fat percentage estimated at 38% due to recent illness.
Inputs: Sex: Female, Weight: 45 kg, Height: 155 cm, Age: 70 years, Body Fat %: 38%
Calculation (using direct method):
Fat Mass = 45 kg * (38 / 100) = 17.1 kg
LBW = 45 kg – 17.1 kg = 27.9 kg
Result: The patient's Lean Body Weight is calculated as 27.9 kg.
Interpretation: In this scenario, the LBW is significantly lower than the total body weight. Dosing drugs based on LBW helps avoid over-sedation or toxicity, considering the patient's reduced capacity for drug clearance and distribution in non-fat tissues. While LBW is crucial, other factors like organ function are also considered.
How to Use This Lean Body Weight Anesthesia Calculator
Our calculator simplifies the process of determining Lean Body Weight (LBW) for anesthesia purposes. Follow these steps:
Select Biological Sex: Choose the patient's biological sex at birth (Male or Female). This is important as body composition can differ.
Enter Total Body Weight: Input the patient's current total body weight in kilograms (kg).
Enter Height: Input the patient's height in centimeters (cm).
Enter Age: Provide the patient's age in years.
Enter Body Fat Percentage (Optional but Recommended): If known, input the patient's body fat percentage. This yields the most accurate LBW calculation. If unknown, you can leave it blank, and the calculator will use predictive formulas that incorporate sex, weight, height, and age.
Click "Calculate LBW": The calculator will process your inputs and display the results.
How to Read Results:
Primary Result (LBW): This is your main calculated Lean Body Weight in kilograms. This value is often used as the basis for drug dosing.
Fat Mass (FM): The calculated amount of fat in kilograms.
Basal Metabolic Rate (BMR): An estimate of the calories your body burns at rest, often correlated with LBW.
Adjusted Body Weight (AdjBW): A weight value sometimes used in dosing obese patients, often calculated as LBW + 0.4 * (TBW – LBW). This can provide a middle ground between LBW and TBW.
Formula Explanation: A brief summary of the calculation method used.
Key Assumptions: Notes about the inputs and method used.
Decision-Making Guidance:
The calculated LBW is a critical piece of information for anesthetic drug selection and dosing. Always consider it alongside other patient factors such as:
Renal function (kidney function)
Hepatic function (liver function)
Cardiac status
Age and overall health status
The specific drug being used and its known pharmacokinetics
Consult with pharmacological guidelines and experienced colleagues when making critical dosing decisions. The calculator is a tool to aid, not replace, clinical judgment.
Key Factors That Affect Lean Body Weight Results
Several factors influence the accuracy and relevance of LBW calculations in an anesthesia context:
Body Composition Variations: Beyond simple body fat percentage, muscle mass, bone density, and fluid status can affect LBW. Athletes, for instance, may have high muscle mass, increasing their LBW.
Hydration Status: Significant fluid shifts (e.g., dehydration, edema) can alter total body weight and, consequently, the calculation of fat mass and LBW, impacting drug distribution.
Method of Body Fat Estimation: If body fat percentage is estimated (e.g., bioelectrical impedance, skinfold calipers), the accuracy of that method directly impacts the calculated LBW. DXA scans are more accurate but less common in acute settings.
Age-Related Changes: Muscle mass tends to decrease with age (sarcopenia), affecting LBW. Conversely, bone density can also change. This is why age is factored into some LBW predictive equations.
Sex Differences: Biological sex influences typical body composition, with males generally having a higher proportion of muscle mass and females a higher proportion of fat mass. This is why sex-specific formulas are used.
Disease States: Conditions like cancer (cachexia), chronic kidney disease, liver failure, or severe burns can dramatically alter body composition, making standard LBW calculations less reliable and necessitating careful clinical assessment.
Medications: Certain medications can affect fluid balance or body composition, indirectly influencing LBW calculations.
Frequently Asked Questions (FAQ) about Lean Body Weight in Anesthesia
Q1: Is Lean Body Weight the same as Ideal Body Weight (IBW)?
No. IBW is a theoretical weight for a person of a specific height, age, and sex, aiming for a healthy BMI. LBW is a calculated value based on the patient's actual body composition (total weight minus fat mass).
Q2: Why is LBW more important than total body weight for some drugs?
Many anesthetic drugs are lipid-soluble or have distribution volumes that correlate better with lean tissue than with total mass. Using LBW helps avoid under- or over-dosing, particularly in patients with very high or very low body fat percentages.
Q3: How is body fat percentage typically measured for clinical use?
Common methods include bioelectrical impedance analysis (BIA), skinfold calipers, and anthropometric measurements. For greater accuracy, Dual-energy X-ray absorptiometry (DXA) is often considered the gold standard, though less practical in immediate anesthetic decision-making.
Q4: What if I don't know the body fat percentage?
Our calculator can use predictive formulas (like the James equation) that estimate LBW based on sex, weight, height, and age when body fat percentage is unknown. However, if body fat is significantly abnormal, clinical judgment remains paramount.
Q5: Does LBW calculation apply to pediatric patients?
Pediatric anesthesia dosing is complex and often relies on specific pediatric nomograms and weight-based calculations. While the concept of body composition is relevant, standard adult LBW formulas are typically not directly applied to infants and children without modification or specialized pediatric guidelines.
Q6: Can LBW change rapidly?
Total body weight can change rapidly due to fluid shifts. However, actual *lean body mass* changes more slowly, typically over weeks or months due to factors like prolonged illness, malnutrition, or intensive training. Fat mass can fluctuate more readily.
Q7: How do I interpret the "Adjusted Body Weight" result?
Adjusted Body Weight (AdjBW) is a method used by some clinicians for obese patients. It's calculated as LBW + 0.4 * (Total Body Weight – LBW). It represents a weight value that is higher than LBW but lower than total body weight, attempting to balance the distribution of certain drugs more accurately than using only TBW or LBW.
Q8: Are there specific drugs where LBW is particularly critical?
Yes, especially for drugs with a narrow therapeutic index or those primarily distributed in total body water, like many neuromuscular blockers, certain sedatives (e.g., propofol), opioids, and vasopressors. Dosing these based on LBW can prevent adverse events.
Learn more about best practices and risk mitigation in anesthetic procedures.
function isNumeric(value) {
return !isNaN(parseFloat(value)) && isFinite(value);
}
function validateInput(id, errorId, min, max) {
var input = document.getElementById(id);
var errorDisplay = document.getElementById(errorId);
var value = parseFloat(input.value);
errorDisplay.textContent = "; // Clear previous error
if (input.value === ") {
// Allow empty for bodyFatPercentage, but others require value
if (id !== 'bodyFatPercentage') {
errorDisplay.textContent = 'This field is required.';
return false;
}
} else if (!isNumeric(input.value)) {
errorDisplay.textContent = 'Please enter a valid number.';
return false;
} else if (value < 0) {
errorDisplay.textContent = 'Value cannot be negative.';
return false;
} else if (min !== undefined && value max) {
errorDisplay.textContent = 'Value cannot be greater than ' + max + '.';
return false;
}
return true;
}
function calculateLBW() {
var gender = document.getElementById('gender').value;
var weightKg = document.getElementById('weightKg').value;
var heightCm = document.getElementById('heightCm').value;
var age = document.getElementById('age').value;
var bodyFatPercentage = document.getElementById('bodyFatPercentage').value;
var resultsContainer = document.getElementById('results-container');
var mainResultDisplay = document.getElementById('main-result');
var fatMassDisplay = document.getElementById('fatMass');
var bmrDisplay = document.getElementById('bmr');
var adjustedBWDisplay = document.getElementById('adjustedBW');
var formulaExplanationDisplay = document.getElementById('formulaExplanation');
var keyAssumptionsDisplay = document.getElementById('keyAssumptions');
// Validation
var isValidWeight = validateInput('weightKg', 'weightKgError', 0);
var isValidHeight = validateInput('heightCm', 'heightCmError', 0);
var isValidAge = validateInput('age', 'ageError', 0);
var isValidBodyFat = true; // Body fat is optional
if (bodyFatPercentage !== ") {
isValidBodyFat = validateInput('bodyFatPercentage', 'bodyFatPercentageError', 0, 100);
}
if (!isValidWeight || !isValidHeight || !isValidAge || !isValidBodyFat) {
resultsContainer.style.display = 'none';
return;
}
weightKg = parseFloat(weightKg);
heightCm = parseFloat(heightCm);
age = parseFloat(age);
bodyFatPercentage = parseFloat(bodyFatPercentage);
var lbwKg;
var fatMassKg;
var bmrKcal;
var adjustedBWKg;
var formulaUsed = "";
var assumptions = [];
// Prioritize calculation using body fat percentage if available and valid
if (bodyFatPercentage > 0 && bodyFatPercentage <= 100) {
fatMassKg = weightKg * (bodyFatPercentage / 100);
lbwKg = weightKg – fatMassKg;
formulaUsed = "LBW = Total Body Weight – Fat Mass (calculated using provided Body Fat Percentage)";
assumptions.push("Calculation based on provided Body Fat Percentage.");
} else {
// Use predictive formulas if body fat percentage is not provided or invalid
if (gender === 'male') {
lbwKg = (0.407 * weightKg) + (0.267 * heightCm) – (0.00054 * age) + 4.0085;
formulaUsed = "LBW = (0.407 * Weight) + (0.267 * Height) – (0.00054 * Age) + 4.0085 (James Equation for Males)";
} else { // Female
lbwKg = (0.252 * weightKg) + (0.186 * heightCm) – (0.00074 * age) + 2.0416;
formulaUsed = "LBW = (0.252 * Weight) + (0.186 * Height) – (0.00074 * Age) + 2.0416 (James Equation for Females)";
}
assumptions.push("Calculation based on predictive formula (e.g., James Equation) as Body Fat Percentage was not provided or invalid.");
fatMassKg = weightKg – lbwKg; // Estimate fat mass based on the predictive LBW
}
// Ensure LBW is not negative or unreasonably low
if (lbwKg < 0) lbwKg = 0;
if (fatMassKg < 0) fatMassKg = 0;
// Calculate BMR using Harris-Benedict equation (often correlated with LBW)
// Using revised Harris-Benedict
var bmrMale = (13.397 * lbwKg) + (4.799 * (heightCm / 100 * 3.28084)) – (5.677 * age) + 88.362; // height in meters, converted to feet
var bmrFemale = (9.247 * lbwKg) + (3.098 * (heightCm / 100 * 3.28084)) – (4.330 * age) + 447.593; // height in meters, converted to feet
if (gender === 'male') {
bmrKcal = bmrMale;
} else {
bmrKcal = bmrFemale;
}
// Calculate Adjusted Body Weight
adjustedBWKg = lbwKg + 0.4 * (weightKg – lbwKg);
if (adjustedBWKg < lbwKg) adjustedBWKg = lbwKg; // Ensure AdjBW is not less than LBW
// Display Results
mainResultDisplay.textContent = lbwKg.toFixed(2) + ' kg';
fatMassDisplay.innerHTML = 'Fat Mass: ' + fatMassKg.toFixed(2) + ' kg';
bmrDisplay.innerHTML = 'BMR: ' + bmrKcal.toFixed(0) + ' kcal';
adjustedBWDisplay.innerHTML = 'Adj. BW: ' + adjustedBWKg.toFixed(2) + ' kg';
formulaExplanationDisplay.textContent = "Formula Used: " + formulaUsed;
keyAssumptionsDisplay.textContent = "Key Assumptions: Biological Sex: " + (gender === 'male' ? 'Male' : 'Female') + ", " + assumptions.join(" ");
resultsContainer.style.display = 'block';
// Update chart and table
updateChart(weightKg, lbwKg);
updateTable(weightKg, lbwKg);
}
function updateChart(totalWeight, lbw) {
var ctx = document.getElementById('lbwChart').getContext('2d');
// Destroy previous chart instance if it exists
if (window.lbwChartInstance) {
window.lbwChartInstance.destroy();
}
var chartData = {
labels: ['Weight Category', 'Lean Body Weight'],
datasets: [{
label: 'Weight (kg)',
data: [totalWeight, lbw],
backgroundColor: [
'rgba(0, 74, 153, 0.6)', // Primary blue for Total Weight
'rgba(40, 167, 69, 0.6)' // Success green for LBW
],
borderColor: [
'rgba(0, 74, 153, 1)',
'rgba(40, 167, 69, 1)'
],
borderWidth: 1
}]
};
window.lbwChartInstance = new Chart(ctx, {
type: 'bar',
data: chartData,
options: {
responsive: true,
maintainAspectRatio: false,
scales: {
y: {
beginAtZero: true,
title: {
display: true,
text: 'Weight (kg)'
}
}
},
plugins: {
legend: {
display: true,
position: 'top',
},
title: {
display: true,
text: 'Comparison: Total Weight vs. Lean Body Weight'
}
}
}
});
}
function updateTable(totalWeight, lbw) {
var tableBody = document.getElementById('typicalRangesTableBody');
tableBody.innerHTML = "; // Clear previous content
var bfPercent = (lbw / totalWeight) * 100;
var fatMass = totalWeight – lbw;
var row1 = tableBody.insertRow();
row1.insertCell(0).textContent = 'Total Body Weight';
row1.insertCell(1).textContent = 'kg';
row1.insertCell(2).textContent = totalWeight.toFixed(2);
row1.insertCell(3).textContent = '-';
var row2 = tableBody.insertRow();
row2.insertCell(0).textContent = 'Fat Mass';
row2.insertCell(1).textContent = 'kg';
row2.insertCell(2).textContent = fatMass.toFixed(2);
row2.insertCell(3).textContent = '-';
var row3 = tableBody.insertRow();
row3.insertCell(0).textContent = 'Lean Body Weight';
row3.insertCell(1).textContent = 'kg';
row3.insertCell(2).textContent = lbw.toFixed(2);
row3.insertCell(3).textContent = lbw.toFixed(2); // Same as calculated LBW
var row4 = tableBody.insertRow();
row4.insertCell(0).textContent = 'Body Fat %';
row4.insertCell(1).textContent = '%';
row4.insertCell(2).textContent = isNaN(bfPercent) ? '-' : bfPercent.toFixed(1);
row4.insertCell(3).textContent = isNaN(bfPercent) ? '-' : bfPercent.toFixed(1);
}
function resetForm() {
document.getElementById('gender').value = 'male';
document.getElementById('weightKg').value = ";
document.getElementById('heightCm').value = ";
document.getElementById('age').value = ";
document.getElementById('bodyFatPercentage').value = ";
document.getElementById('weightKgError').textContent = ";
document.getElementById('heightCmError').textContent = ";
document.getElementById('ageError').textContent = ";
document.getElementById('bodyFatPercentageError').textContent = ";
document.getElementById('results-container').style.display = 'none';
// Clear chart
if (window.lbwChartInstance) {
window.lbwChartInstance.destroy();
window.lbwChartInstance = null;
}
var canvas = document.getElementById('lbwChart');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
// Clear table
document.getElementById('typicalRangesTableBody').innerHTML = ";
}
function copyToClipboard(text) {
navigator.clipboard.writeText(text).then(function() {
alert('Results copied to clipboard!');
}, function() {
alert('Failed to copy results.');
});
}
function copyResults() {
var mainResult = document.getElementById('main-result').innerText;
var fatMass = document.getElementById('fatMass').innerText.replace('Fat Mass: ', ");
var bmr = document.getElementById('bmr').innerText.replace('BMR: ', ");
var adjustedBW = document.getElementById('adjustedBW').innerText.replace('Adj. BW: ', ");
var formula = document.getElementById('formulaExplanation').innerText;
var assumptions = document.getElementById('keyAssumptions').innerText;
var chartTitle = document.querySelector('.chart-section caption').innerText;
var tableCaption = document.querySelector('.table-section caption').innerText;
var textToCopy = "— Lean Body Weight Anesthesia Calculation Results —\n\n";
textToCopy += "Primary Result (LBW): " + mainResult + "\n";
textToCopy += "Fat Mass: " + fatMass + "\n";
textToCopy += "Estimated BMR: " + bmr + "\n";
textToCopy += "Adjusted Body Weight: " + adjustedBW + "\n\n";
textToCopy += formula + "\n";
textToCopy += assumptions + "\n\n";
textToCopy += "— Data Summary —\n";
textToCopy += chartTitle + "\n";
textToCopy += tableCaption + "\n";
copyToClipboard(textToCopy);
}
// Load Chart.js if not already loaded or use a placeholder if no external libs allowed
// Since no external libraries are allowed, we will draw directly or use pure SVG.
// For this example, we'll use a simplified drawing approach or indicate this limitation.
// As per instructions, we should use native or pure SVG.
// I'll proceed with and assume Chart.js is NOT available externally.
// A full native canvas implementation without a library is complex for bars.
// Reverting to a simpler note or a basic rendering placeholder if Chart.js is forbidden.
// *** REVISED: Assuming Chart.js library IS NOT available as per prompt. ***
// *** Implementing a basic placeholder message or attempting direct canvas drawing ***
// Direct canvas drawing for bar charts is quite involved.
// If Chart.js is truly forbidden, a real implementation would require significant JS drawing code.
// For demonstration, I'll assume a context where Chart.js CAN be loaded for the canvas element.
// If not, the chart part would need a full manual canvas drawing implementation.
// The prompt says "❌ No external chart libraries", so Chart.js IS forbidden.
// I will leave the canvas element and provide a note that native drawing is required.
// **** EDIT: The prompt implies *I* should provide the solution. A full native canvas bar chart is too much.
// I will add a placeholder comment and a function stub.
// Let's assume the user might *later* add a library like Chart.js to the canvas, or I should provide that code.
// I'll assume the simplest interpretation for delivery: the canvas element exists, and the JS function is called.
// The JS code *itself* will draw on canvas if a library is not used.
// Given the complexity, I will provide the Chart.js structure and note its absence.
// *** FINAL DECISION: Use a placeholder for chart logic and focus on calculator and article.
// The requirement for *dynamic chart* without external libraries means manual canvas drawing.
// This is very complex to implement fully and cleanly within this format.
// I will stub out the chart drawing function and ensure the calculator calls it.
// Placeholder for native canvas drawing if Chart.js is forbidden.
// A full implementation requires manual pixel drawing based on data.
function drawNativeCanvasChart(data, canvasId) {
var canvas = document.getElementById(canvasId);
if (!canvas || !canvas.getContext) {
console.error("Canvas not supported or not found.");
return;
}
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height); // Clear previous drawing
var chartWidth = canvas.width;
var chartHeight = canvas.height;
var barWidth = 30;
var barSpacing = 20;
var maxValue = Math.max(data[0].value, data[1].value);
if (maxValue === 0) maxValue = 1; // Avoid division by zero
var label1 = data[0].label;
var value1 = data[0].value;
var color1 = data[0].color;
var label2 = data[1].label;
var value2 = data[1].value;
var color2 = data[1].color;
// Drawing bars
var totalBarWidth = chartWidth * 0.6;
var barWidthActual = (totalBarWidth – barSpacing * 2) / 2;
var startXBar1 = chartWidth * 0.2;
var startXBar2 = startXBar1 + barWidthActual + barSpacing;
// Bar 1
var barHeight1 = (value1 / maxValue) * (chartHeight * 0.7);
ctx.fillStyle = color1;
ctx.fillRect(startXBar1, chartHeight – barHeight1 – 40, barWidthActual, barHeight1);
ctx.fillStyle = '#333';
ctx.textAlign = 'center';
ctx.fillText(label1, startXBar1 + barWidthActual / 2, chartHeight – 20);
ctx.fillText(value1.toFixed(1) + ' kg', startXBar1 + barWidthActual / 2, chartHeight – barHeight1 – 45);
// Bar 2
var barHeight2 = (value2 / maxValue) * (chartHeight * 0.7);
ctx.fillStyle = color2;
ctx.fillRect(startXBar2, chartHeight – barHeight2 – 40, barWidthActual, barHeight2);
ctx.fillStyle = '#333';
ctx.fillText(label2, startXBar2 + barWidthActual / 2, chartHeight – 20);
ctx.fillText(value2.toFixed(1) + ' kg', startXBar2 + barWidthActual / 2, chartHeight – barHeight2 – 45);
// Y-axis scale
ctx.beginPath();
ctx.moveTo(chartWidth * 0.15, chartHeight * 0.1);
ctx.lineTo(chartWidth * 0.15, chartHeight * 0.85);
ctx.strokeStyle = '#666';
ctx.stroke();
// Add scale markers (simplified)
ctx.fillStyle = '#666';
ctx.textAlign = 'right';
ctx.fillText(maxValue.toFixed(0), chartWidth * 0.13, chartHeight * 0.15);
ctx.fillText((maxValue/2).toFixed(0), chartWidth * 0.13, chartHeight * 0.5);
ctx.fillText('0', chartWidth * 0.13, chartHeight * 0.85);
// Chart Title
ctx.fillStyle = '#004a99';
ctx.font = 'bold 16px Segoe UI, Tahoma, Geneva, Verdana, sans-serif';
ctx.textAlign = 'center';
ctx.fillText('Comparison: Total Weight vs. Lean Body Weight', chartWidth / 2, 25);
}
function updateChart(totalWeight, lbw) {
var chartData = [
{ label: 'Total Weight', value: totalWeight, color: 'rgba(0, 74, 153, 0.7)' },
{ label: 'Lean Body Weight', value: lbw, color: 'rgba(40, 167, 69, 0.7)' }
];
drawNativeCanvasChart(chartData, 'lbwChart');
}
// Initial calculation on load for default values if any
// calculateLBW(); // Commented out to avoid calculation on empty initial load without user interaction.