This calculator helps you estimate the required size of a septic tank and drainfield based on the number of bedrooms in your home and local regulations. Proper sizing is crucial for effective wastewater treatment and to prevent system failures.
A slower rate (higher number) requires a larger drainfield.
This value depends on your soil type and is often provided by local health departments. Consult your local regulations.
.septic-calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ccc;
border-radius: 8px;
background-color: #f9f9f9;
}
.septic-calculator-container h2 {
text-align: center;
margin-bottom: 15px;
color: #333;
}
.septic-calculator-container p {
margin-bottom: 20px;
line-height: 1.5;
color: #555;
}
.calculator-inputs .form-group {
margin-bottom: 15px;
}
.calculator-inputs label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.calculator-inputs input[type="number"] {
width: calc(100% – 22px);
padding: 10px;
border: 1px solid #ddd;
border-radius: 4px;
box-sizing: border-box;
}
.calculator-inputs small {
display: block;
margin-top: 5px;
font-size: 0.85em;
color: #777;
}
.septic-calculator-container button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 16px;
cursor: pointer;
transition: background-color 0.3s ease;
}
.septic-calculator-container button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
color: #333;
text-align: center;
font-size: 1.1em;
}
.calculator-result strong {
color: #007bff;
}
function calculateSepticSize() {
var bedrooms = parseInt(document.getElementById("numberOfBedrooms").value);
var percolationRate = parseFloat(document.getElementById("percolationRate").value);
var soilAbsorptionRate = parseFloat(document.getElementById("soilAbsorptionRate").value);
var resultDiv = document.getElementById("septicResult");
resultDiv.innerHTML = ""; // Clear previous results
// Basic validation
if (isNaN(bedrooms) || bedrooms <= 0) {
resultDiv.innerHTML = "Please enter a valid number of bedrooms.";
return;
}
if (isNaN(percolationRate) || percolationRate <= 0) {
resultDiv.innerHTML = "Please enter a valid percolation rate.";
return;
}
if (isNaN(soilAbsorptionRate) || soilAbsorptionRate <= 0) {
resultDiv.innerHTML = "Please enter a valid soil absorption rate.";
return;
}
// — Septic Tank Size Calculation —
// Typical daily wastewater flow is assumed to be 75 gallons per bedroom per day.
// Tank size is often required to be 1.5 to 2 times the daily flow, or a minimum size (e.g., 1000 gallons).
// Local codes are paramount here. This is a simplified estimation.
var dailyFlow = bedrooms * 75; // Gallons per day
var minTankGallons = 1000; // Minimum recommended tank size
var estimatedTankSize = dailyFlow * 1.5; // Using 1.5 times daily flow for estimation
if (estimatedTankSize 15 && percolationRate 30 && percolationRate 60) {
drainfieldAreaMultiplier = 2.0; // Significantly larger area for very slow percolation
}
// Note: Very fast percolation (e.g., < 5 min/inch) might require different designs (e.g., mound systems) or shallower drainfields, not just larger ones.
// This simplified model focuses on area expansion for slower rates.
estimatedDrainfieldArea = estimatedDrainfieldArea * drainfieldAreaMultiplier;
// — Display Results —
var resultHTML = "
Estimated Septic System Requirements:
";
resultHTML += "Based on " + bedrooms + " bedrooms:";
resultHTML += "Estimated Daily Wastewater Flow: " + dailyFlow.toFixed(0) + " gallons/day";
resultHTML += "Estimated Minimum Septic Tank Size: " + estimatedTankSize.toFixed(0) + " gallons";
resultHTML += "Estimated Minimum Drainfield Area: " + estimatedDrainfieldArea.toFixed(2) + " square feet";
resultHTML += "Disclaimer: This calculator provides a simplified estimation only. Actual septic system requirements are determined by local health codes, specific site conditions (including soil types and topography), and may require professional assessment by a licensed engineer or contractor. Always consult your local authorities for definitive requirements.";
resultDiv.innerHTML = resultHTML;
}