Garden Hose Flow Rate Calculator

Garden Hose Flow Rate Calculator

Estimate the Gallons Per Minute (GPM) based on hose dimensions and water pressure.

1/2 inch (Standard) 5/8 inch (Common) 3/4 inch (Heavy Duty) 1 inch (Commercial)

Avg. residential is 40-60 PSI

Estimated Flow Rate:

0.00 GPM

(0.00 Liters Per Minute)

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function calculateFlowRate() { var d = parseFloat(document.getElementById('hoseDiameter').value); var l = parseFloat(document.getElementById('hoseLength').value); var p = parseFloat(document.getElementById('psiInput').value); var resultArea = document.getElementById('resultArea'); if (isNaN(l) || isNaN(p) || l <= 0 || p <= 0) { alert("Please enter valid positive numbers for length and pressure."); return; } // Empirical formula for water flow in small pipes (Hazen-Williams simplification) // GPM = (29.84 * d^2 * sqrt(PSI)) / sqrt(Length/Factor) // Using a standard friction coefficient for smooth rubber/vinyl // A common approximation for garden hoses: var flowRate = (Math.pow(d, 2.63) * 15.1 * Math.pow((p / l), 0.54)); // Adjustments for real-world friction loss in standard garden hoses var gpm = flowRate; var lpm = gpm * 3.78541; // Calculate fill time for 100 gallons var fillTimeMinutes = 100 / gpm; document.getElementById('gpmResult').innerHTML = gpm.toFixed(2) + " GPM"; document.getElementById('lpmResult').innerHTML = "(" + lpm.toFixed(2) + " Liters Per Minute)"; document.getElementById('fillTimeText').innerHTML = "At this rate, it would take approximately " + fillTimeMinutes.toFixed(1) + " minutes to fill a 100-gallon pool."; resultArea.style.display = 'block'; }

Understanding Garden Hose Flow Rate (GPM)

Whether you are setting up a temporary irrigation system, filling a swimming pool, or choosing a pressure washer, knowing the flow rate of your garden hose is essential. Flow rate is typically measured in Gallons Per Minute (GPM) or Liters Per Minute (LPM) and represents the volume of water moving through the hose at any given time.

Key Factors That Influence Water Flow

Several physical variables determine how much water actually reaches the end of your nozzle. It is rarely as simple as the pressure at the spigot.

• Hose Diameter: This is the most critical factor. A 3/4-inch hose can deliver nearly double the water of a 1/2-inch hose because the internal cross-sectional area is significantly larger.
• Hose Length: Friction is the enemy of flow. As water travels through the hose, it rubs against the interior walls, creating friction loss. The longer the hose, the lower the pressure and flow at the outlet.
• Static Water Pressure (PSI): Measured in Pounds per Square Inch, this is the force pushing the water. Most residential systems operate between 40 and 60 PSI.
• Couplings and Kinks: Any narrowing of the path (like a crushed coupling or a tight bend) drastically restricts GPM, regardless of the hose's main diameter.

Example Flow Rate Scenarios

To help you visualize how these variables interact, consider these typical estimates for a standard 50-foot hose at 40 PSI:

Hose Diameter	Estimated GPM	Best Use Case
1/2 Inch	6 – 8 GPM	Light watering, hanging baskets
5/8 Inch	9 – 12 GPM	General lawn care, car washing
3/4 Inch	18 – 23 GPM	Commercial use, filling large pools

How to Manually Measure Your Flow Rate

If you want to verify the calculator's results, you can perform a "Bucket Test" at home:

1. Get a 5-gallon bucket.
2. Turn your hose on to its maximum setting.
3. Time exactly how many seconds it takes to fill the bucket to the 5-gallon mark.
4. Use this formula: (5 / Seconds) × 60 = GPM.

For example, if your bucket fills in 30 seconds, your flow rate is 10 GPM (5 divided by 30 is 0.166; 0.166 multiplied by 60 equals 10).

Why Does Flow Rate Matter?

If you are installing an automatic sprinkler system, you must know your GPM to ensure you don't put too many sprinkler heads on one zone. If the heads require 15 GPM but your hose only provides 10 GPM, the heads will not pop up or cover the intended distance. Similarly, knowing flow rate helps prevent damage to high-end pressure washers that require a specific minimum intake of water to cool the pump.