Maintaining the correct chlorine level in your swimming pool is crucial for ensuring clean, safe, and sparkling water. Chlorine acts as a sanitizer, killing bacteria, viruses, and algae that can contaminate your pool. Too little chlorine can lead to cloudy water, algae growth, and potential health risks, while too much can cause skin and eye irritation, damage pool equipment, and fade liners.
This Swimming Pool Chlorine Calculator helps you determine the precise amount of chlorine product needed to achieve your desired free chlorine (FC) level. It takes into account your pool's volume, current chlorine levels, and the specific type and strength of chlorine product you are using.
Understanding Free Chlorine (FC)
Free Chlorine (FC) is the active form of chlorine available to sanitize your pool water. It's what you measure with your test kit. The ideal FC range for most pools is 1-3 parts per million (ppm). Factors like sunlight, bather load, rain, and organic debris consume free chlorine, which is why regular testing and replenishment are necessary.
Types of Chlorine Products
Liquid Sodium Hypochlorite (Bleach): Typically 10-12.5% available chlorine. It's fast-acting, doesn't add cyanuric acid (CYA), and is relatively inexpensive. However, it has a short shelf life and can raise pH.
Dichlor (Sodium Dichloro-s-triazinetrione): Granular, typically 56% available chlorine. It's stabilized, meaning it contains CYA, which protects chlorine from UV degradation. Good for shocking and regular chlorination, but adds CYA.
Cal-Hypo (Calcium Hypochlorite): Granular, typically 65-73% available chlorine. It's unstabilized, so it doesn't add CYA, but it does add calcium hardness. Good for shocking.
Trichlor (Trichloro-s-triazinetrione): Tablets or sticks, typically 90% available chlorine. It's stabilized and very convenient for feeders, but it's highly acidic and adds a significant amount of CYA, which can lead to "chlorine lock" if levels get too high.
How to Use the Calculator
Measure Your Pool Dimensions: For rectangular pools, you'll need length, width, and average depth. For round pools, diameter and average depth. For oval pools, length, width, and average depth. If you already know your pool's volume, select "Custom Volume".
Test Your Water: Use a reliable test kit to determine your current Free Chlorine (FC) level in ppm.
Determine Your Target FC: Most experts recommend 1-3 ppm for regular maintenance. For shocking, you might aim for 10 ppm or higher.
Select Your Chlorine Product: Choose the type of chlorine you're using from the dropdown. The calculator will pre-fill a common strength, but you can adjust it if your product has a different percentage.
Click "Calculate": The calculator will provide the recommended amount of chlorine product to add to your pool.
Important Considerations
Safety First: Always handle chlorine products with care. Wear protective gloves and eyewear. Never mix different types of chlorine, as this can cause dangerous reactions.
Test Regularly: Pool chemistry can change quickly. Test your water daily or every few days, especially after heavy use or rain.
CYA Levels: If using stabilized chlorine (Dichlor or Trichlor), monitor your Cyanuric Acid (CYA) levels. High CYA can reduce chlorine effectiveness.
Shocking: For severe algae or very cloudy water, you may need to "shock" your pool by raising the FC level significantly (e.g., 10-20 ppm).
Circulation: Ensure your pool pump is running to circulate the water and distribute the chlorine evenly after adding it.
Please enter your pool details and click 'Calculate'.
function updatePoolShapeInputs() {
var poolShape = document.getElementById('poolShape').value;
document.getElementById('rectangularInputs').style.display = 'none';
document.getElementById('roundInputs').style.display = 'none';
document.getElementById('ovalInputs').style.display = 'none';
document.getElementById('customVolumeInput').style.display = 'none';
if (poolShape === 'rectangular') {
document.getElementById('rectangularInputs').style.display = 'block';
} else if (poolShape === 'round') {
document.getElementById('roundInputs').style.display = 'block';
} else if (poolShape === 'oval') {
document.getElementById('ovalInputs').style.display = 'block';
} else if (poolShape === 'custom') {
document.getElementById('customVolumeInput').style.display = 'block';
}
}
function updateChlorineProductStrength() {
var productType = document.getElementById('chlorineProductType').value;
var strengthInput = document.getElementById('chlorineProductStrength');
switch (productType) {
case 'liquid_sodium_hypochlorite':
strengthInput.value = 10; // Common for household bleach, can be 12.5% for pool-specific
break;
case 'dichlor_granular':
strengthInput.value = 56;
break;
case 'cal_hypo_granular':
strengthInput.value = 65;
break;
case 'trichlor_tablets':
strengthInput.value = 90;
break;
case 'custom':
// User will manually enter, no default change
break;
}
}
function calculateChlorine() {
var poolShape = document.getElementById('poolShape').value;
var poolVolume = 0;
var GALLONS_PER_CUBIC_FOOT = 7.48052;
var PI = Math.PI;
// Calculate Pool Volume
if (poolShape === 'rectangular') {
var length = parseFloat(document.getElementById('poolLength').value);
var width = parseFloat(document.getElementById('poolWidth').value);
var avgDepth = parseFloat(document.getElementById('poolAvgDepth').value);
if (isNaN(length) || isNaN(width) || isNaN(avgDepth) || length <= 0 || width <= 0 || avgDepth <= 0) {
document.getElementById('chlorineResult').innerHTML = 'Please enter valid positive numbers for rectangular pool dimensions.';
return;
}
poolVolume = length * width * avgDepth * GALLONS_PER_CUBIC_FOOT;
} else if (poolShape === 'round') {
var diameter = parseFloat(document.getElementById('poolDiameter').value);
var avgDepth = parseFloat(document.getElementById('roundPoolAvgDepth').value);
if (isNaN(diameter) || isNaN(avgDepth) || diameter <= 0 || avgDepth <= 0) {
document.getElementById('chlorineResult').innerHTML = 'Please enter valid positive numbers for round pool dimensions.';
return;
}
var radius = diameter / 2;
poolVolume = PI * radius * radius * avgDepth * GALLONS_PER_CUBIC_FOOT;
} else if (poolShape === 'oval') {
var length = parseFloat(document.getElementById('ovalPoolLength').value);
var width = parseFloat(document.getElementById('ovalPoolWidth').value);
var avgDepth = parseFloat(document.getElementById('ovalPoolAvgDepth').value);
if (isNaN(length) || isNaN(width) || isNaN(avgDepth) || length <= 0 || width <= 0 || avgDepth <= 0) {
document.getElementById('chlorineResult').innerHTML = 'Please enter valid positive numbers for oval pool dimensions.';
return;
}
// A common approximation factor for oval pools is 0.89 for the area of the equivalent rectangle.
// So, L * W * AvgDepth * 0.89 * GALLONS_PER_CUBIC_FOOT, which is approx L * W * AvgDepth * 6.7
poolVolume = length * width * avgDepth * 6.7;
} else if (poolShape === 'custom') {
poolVolume = parseFloat(document.getElementById('customPoolVolume').value);
if (isNaN(poolVolume) || poolVolume <= 0) {
document.getElementById('chlorineResult').innerHTML = 'Please enter a valid positive number for custom pool volume.';
return;
}
}
var currentFC = parseFloat(document.getElementById('currentFreeChlorine').value);
var targetFC = parseFloat(document.getElementById('targetFreeChlorine').value);
var chlorineProductType = document.getElementById('chlorineProductType').value;
var chlorineProductStrength = parseFloat(document.getElementById('chlorineProductStrength').value);
if (isNaN(currentFC) || isNaN(targetFC) || isNaN(chlorineProductStrength) || currentFC < 0 || targetFC <= 0 || chlorineProductStrength 100) {
document.getElementById('chlorineResult').innerHTML = 'Please enter valid positive numbers for chlorine levels and product strength (1-100%).';
return;
}
if (targetFC <= currentFC) {
document.getElementById('chlorineResult').innerHTML = 'Your current Free Chlorine level is already at or above your target. No chlorine addition is needed.';
return;
}
var ppmToRaise = targetFC – currentFC;
var chlorineStrengthDecimal = chlorineProductStrength / 100;
// Constants for calculation
// To raise FC by 1 ppm in 10,000 gallons, you need 0.0834 lbs of 100% chlorine.
var LBS_100_CHLORINE_PER_10K_GAL_PER_1_PPM = 0.0834;
var OUNCES_PER_POUND = 16;
var GRAMS_PER_POUND = 453.592;
var resultMessage = '
Calculation Results:
';
resultMessage += 'Estimated Pool Volume: ' + poolVolume.toFixed(0) + ' gallons';
resultMessage += 'Free Chlorine to raise: ' + ppmToRaise.toFixed(1) + ' ppm';
if (chlorineProductType === 'liquid_sodium_hypochlorite') {
// Common rule of thumb: 13 fl oz of 10% liquid chlorine per 10,000 gallons to raise FC by 1 ppm.
// Scale this based on the actual product strength.
var liquidChlorineFlOz = (ppmToRaise * (poolVolume / 10000) * 13) / (chlorineProductStrength / 10);
resultMessage += 'Add ' + liquidChlorineFlOz.toFixed(1) + ' fluid ounces of ' + chlorineProductStrength + '% Liquid Chlorine.';
resultMessage += '(Approximately ' + (liquidChlorineFlOz / 128).toFixed(2) + ' gallons)';
} else {
// Calculate pounds of 100% chlorine needed
var poundsOf100PercentChlorine = ppmToRaise * (poolVolume / 10000) * LBS_100_CHLORINE_PER_10K_GAL_PER_1_PPM;
// Calculate pounds of the specific granular product needed
var poundsOfProduct = poundsOf100PercentChlorine / chlorineStrengthDecimal;
var ouncesOfProduct = poundsOfProduct * OUNCES_PER_POUND;
var gramsOfProduct = poundsOfProduct * GRAMS_PER_POUND;
resultMessage += 'Add ' + ouncesOfProduct.toFixed(1) + ' ounces (weight) of ' + chlorineProductStrength + '% ' + chlorineProductType.replace(/_/g, ' ').replace('granular', 'Granular').replace('tablets', 'Tablets') + '.';
resultMessage += '(Approximately ' + gramsOfProduct.toFixed(0) + ' grams)';
}
document.getElementById('chlorineResult').innerHTML = resultMessage;
}
// Initialize inputs on page load
window.onload = function() {
updatePoolShapeInputs();
updateChlorineProductStrength();
};