function toggleInputs() {
var shape = document.getElementById('pondShape').value;
if (shape === 'rectangular') {
document.getElementById('rectInputs').style.display = 'block';
document.getElementById('circInputs').style.display = 'none';
} else {
document.getElementById('rectInputs').style.display = 'none';
document.getElementById('circInputs').style.display = 'block';
}
}
function calculatePondFlow() {
var shape = document.getElementById('pondShape').value;
var depth = parseFloat(document.getElementById('pondDepth').value);
var turnover = parseFloat(document.getElementById('turnoverHours').value);
var volumeGallons = 0;
if (isNaN(depth) || depth <= 0) {
alert("Please enter a valid depth.");
return;
}
if (shape === 'rectangular') {
var length = parseFloat(document.getElementById('pondLength').value);
var width = parseFloat(document.getElementById('pondWidth').value);
if (isNaN(length) || isNaN(width) || length <= 0 || width <= 0) {
alert("Please enter valid length and width.");
return;
}
// L * W * D * 7.48 (cubic ft to gallons)
volumeGallons = length * width * depth * 7.48;
} else {
var diameter = parseFloat(document.getElementById('pondDiameter').value);
if (isNaN(diameter) || diameter <= 0) {
alert("Please enter a valid diameter.");
return;
}
var radius = diameter / 2;
// PI * R^2 * D * 7.48
volumeGallons = Math.PI * Math.pow(radius, 2) * depth * 7.48;
}
var flowRateGPH = volumeGallons / turnover;
var suggestedPump = flowRateGPH * 1.25; // Adding 25% for head pressure friction loss
document.getElementById('resVolume').innerText = Math.round(volumeGallons).toLocaleString();
document.getElementById('resGPH').innerText = Math.round(flowRateGPH).toLocaleString();
document.getElementById('resPump').innerText = Math.round(suggestedPump).toLocaleString();
document.getElementById('pondResult').style.display = 'block';
}
Understanding Pond Flow Rate: A Comprehensive Guide
Calculating the correct flow rate for your pond is critical for maintaining a healthy ecosystem. Whether you are keeping prize-winning Koi or a simple decorative water garden, water circulation prevents stagnation, increases oxygen levels, and ensures that your filtration system can effectively process waste.
How to Use the Pond Flow Rate Calculator
To determine the equipment you need, you first need to understand the total volume of your pond and how often that water needs to pass through a filter. This calculator simplifies the process by converting physical dimensions into liquid volume and then applying industry-standard turnover rates.
Step 1: Select your pond's shape (Rectangular or Circular).
Step 2: Enter the dimensions in feet. For irregular shapes, use the "average" length and width.
Step 3: Input the average depth. Most ponds have varying depths; use the mean depth for accuracy.
Step 4: Select your turnover time based on your fish load.
What is "Turnover Rate"?
Turnover rate refers to the amount of time it takes for every drop of water in your pond to pass through the filtration system once. The more biological load (fish waste, decaying plants) you have, the faster the turnover needs to be.
Pond Type
Recommended Turnover
Koi Ponds
Once every 1 to 1.5 hours
Standard Goldfish Pond
Once every 2 hours
Water Garden (Plants Only)
Once every 4 hours
The Math Behind the Calculation
The calculation uses the following physical constants:
Volume (Rectangular): Length (ft) × Width (ft) × Average Depth (ft) × 7.48 = Total Gallons
Volume (Circular): π × Radius² (ft) × Average Depth (ft) × 7.48 = Total Gallons
Flow Rate: Total Gallons / Turnover Time (Hours) = GPH
Example Calculation
Imagine a rectangular pond that is 10 feet long, 8 feet wide, and 3 feet deep. You plan to keep several Koi fish, so you want a 1-hour turnover rate.
Volume: 10 × 8 × 3 = 240 cubic feet.
Conversion: 240 × 7.48 = 1,795.2 Gallons.
Flow Rate: 1,795.2 / 1 hour = 1,795 GPH.
Important: Considering Head Pressure
When buying a pump, don't just look at the raw GPH rating. Most pumps are rated at "zero head," meaning they move that much water if there is no resistance. In reality, you have vertical lift (pumping water up to a waterfall) and friction loss from the tubing. Our calculator provides a "Suggested Pump Size" which includes a 25% buffer to account for standard friction loss. If your waterfall is very high (over 5 feet), you may need an even more powerful pump.