Pipe Pressure Loss Calculator (Hazen-Williams)

How to do it

1. 1
   Step 1: Open Pipe Pressure Loss Calculator (Hazen-Williams) and add your input

   Type your numbers or text, add your file, or pick the options you need. Nothing is uploaded: everything stays in your browser.

2. 2
   Step 2: What Pipe Pressure Loss Calculator (Hazen-Williams) does

   Calculate pressure loss and water velocity in a pipe from flow, diameter and material.

3. 3
   Step 3: Read the result and compare

   The result appears at once. Change one value to see how the answer moves, then keep the figure that fits your case.

4. 4
   Step 4: Copy or save it

   Copy the result or download it. For an important decision, confirm it with the official source or an adviser.

About this tool

Enter the flow in gallons per minute, the inside diameter in inches, the pipe roughness coefficient and the length. The calculator gives the water velocity, the friction loss per 100 feet and the total pressure loss.

Formula

Hazen-Williams: loss in psi per foot = 4.52 × Q^1.85 ÷ (C^1.85 × d^4.87), with Q in gpm, d the inside diameter in inches and C the roughness coefficient: about 150 for PEX and copper, 140 for plastic, 130 for older steel and 100 for old cast iron.

Velocity

Velocity in ft/s = 0.4085 × Q ÷ d². Keep it below about 5 to 8 ft/s to limit noise and erosion.

Use

Pick pipe sizes so the total loss, plus the elevation change and fittings, leaves enough pressure at the fixtures. Fittings add an equivalent length.

Worked example

8 gpm through 100 feet of 0.75 inch PEX (C = 150) flows at 5.8 ft/s and loses 8.1 psi.

Tips for best results

Check every box before you rely on a result, because one wrong digit changes the whole answer. Use the exact figures from your payslip, bill, certificate or contract, and keep a note of the date you calculated. Rates, thresholds and rules change from time to time, so for tax, fees and legal matters treat the output as an estimate and confirm with the official source named on this page. You can run as many scenarios as you like; nothing is saved or sent, and refreshing the page clears the boxes.