Determine the ideal grain capacity for your household based on water hardness and usage.
Check your water test report or city data.
Enter 0 if no iron is present. Every 1 ppm of iron equals 4 grains of hardness.
3 Days (Frequent)
7 Days (Recommended)
10 Days (Less Frequent)
14 Days (Maximum)
Recommended Softener Capacity
Compensated Hardness: 0 GPG
Daily Household Requirement: 0 Grains
Total Capacity Needed: 0 Grains
Suggested Unit Size: 32,000 Grains
How to Determine What Size Water Softener You Need
Choosing the correct water softener size is critical for both water quality and appliance longevity. A unit that is too small will regenerate too frequently, wasting water and salt, while a unit that is too large may result in bacteria growth or "channeling" within the resin bed.
The Calculation Formula
The standard formula used by water treatment professionals involves four primary variables:
Daily Water Usage: On average, one person uses 75 to 100 gallons of water per day. We use 75 gallons as a conservative baseline for sizing.
Compensated Hardness: This is your base hardness (GPG) plus an adjustment for iron content. Because iron is harder to remove than calcium, we multiply the Iron PPM by 4 and add it to the hardness.
Regeneration Cycle: Most modern systems are most efficient when they regenerate every 6 to 7 days.
Total Grain Capacity: This is the product of your daily grains needed multiplied by the days between regenerations.
Hardness Levels Explained
Water hardness is usually measured in Grains Per Gallon (GPG) or Parts Per Million (PPM). To convert PPM to GPG, divide the PPM by 17.1.
Slightly Hard: 1.0 – 3.5 GPG
Moderately Hard: 3.5 – 7.0 GPG
Hard: 7.0 – 10.5 GPG
Very Hard: 10.5+ GPG
Standard Unit Sizes
Water softeners are typically sold in fixed grain capacities. Once you calculate your "Total Capacity Needed," you should round up to the nearest standard size:
Capacity (Grains)
Typical Household Size
24,000
1-2 People
32,000
2-4 People
48,000
4-6 People
64,000+
Large Families / High Hardness
Example Calculation
If you have 4 people in your home, water hardness of 10 GPG, and 1 PPM of iron:
Compensated Hardness: 10 + (1 * 4) = 14 GPG
Daily Water Usage: 4 people * 75 gallons = 300 gallons/day
Result: You should purchase at least a 32,000-grain unit.
function calculateSoftenerSize() {
var people = parseFloat(document.getElementById("numPeople").value);
var hardness = parseFloat(document.getElementById("waterHardness").value);
var iron = parseFloat(document.getElementById("ironContent").value);
var days = parseFloat(document.getElementById("regenFrequency").value);
// Validation
if (isNaN(people) || people <= 0) { alert("Please enter a valid number of people."); return; }
if (isNaN(hardness) || hardness < 0) { alert("Please enter a valid hardness value."); return; }
if (isNaN(iron) || iron < 0) { iron = 0; }
// 1. Calculate Compensated Hardness
// Standard rule: Add 4 grains of hardness for every 1 ppm of iron
var compensatedHardness = hardness + (iron * 4);
// 2. Daily Water Usage
// Using standard industry average of 75 gallons per person per day
var dailyUsage = people * 75;
// 3. Daily Softening Requirement (Grains per day)
var dailyGrains = dailyUsage * compensatedHardness;
// 4. Total capacity needed for the selected regeneration cycle
var totalNeeded = dailyGrains * days;
// Display Results
document.getElementById("resCompensated").innerHTML = compensatedHardness.toLocaleString();
document.getElementById("resDailyGrains").innerHTML = Math.round(dailyGrains).toLocaleString();
document.getElementById("resTotalNeeded").innerHTML = Math.round(totalNeeded).toLocaleString();
// Determine Suggested Unit Size
var suggested = "";
if (totalNeeded <= 24000) {
suggested = "24,000 Grains";
} else if (totalNeeded <= 32000) {
suggested = "32,000 Grains";
} else if (totalNeeded <= 48000) {
suggested = "48,000 Grains";
} else if (totalNeeded <= 64000) {
suggested = "64,000 Grains";
} else if (totalNeeded <= 80000) {
suggested = "80,000 Grains";
} else if (totalNeeded <= 110000) {
suggested = "110,000 Grains";
} else {
suggested = "Large Custom/Commercial System Required";
}
document.getElementById("resSuggestedSize").innerHTML = suggested;
document.getElementById("resultsArea").style.display = "block";
}