📐 Pressure Drop Rate
🎯 Flow Velocity
Results Breakdown
Full Calculation Table
| Parameter | Value | Notes |
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How to Use the Pipe Pressure Drop Calculator
Choose the pipe material and the nominal size you already have or are considering. Unlike the pipe sizing calculator, this tool checks a pipe size you specify rather than recommending one.
Enter the design flow rate for this segment and its equivalent length. Include a fitting allowance in the length using the fitting equivalent length calculator if the run has several elbows, tees, or valves.
Click Calculate Pressure Drop to see total pressure drop, the rate per 100 m, and the actual flow velocity at this pipe size.
Compare the velocity result against the usual 0.6 to 1.2 m/s branch target. If pressure drop or velocity is too high, try a larger nominal size and recalculate.
Checking Pressure Drop on a Known Pipe Size
This calculator answers a different question than the pipe sizing calculator. Instead of working backward from a target velocity to find a recommended size, this tool checks the pressure drop and velocity that result from a pipe size you already have in mind, whether from an existing installation, a drawing you are reviewing, or a size you want to confirm before committing to it.
The Hazen-Williams Method
This calculator uses the Hazen-Williams equation, a widely used empirical formula for friction loss in water-based piping that does not require iterating on a friction factor the way the more rigorous Darcy-Weisbach method does. Hazen-Williams is accurate enough for most hydronic design work and is the standard quick-check method taught in Canadian mechanical programs, with roots in the same friction factor research covered in the U.S. Bureau of Reclamation's engineering monograph on friction factors. For glycol mixtures or refrigerant lines, where fluid viscosity differs meaningfully from water, the Darcy-Weisbach calculator gives a more precise result.
Reading the Pressure Drop Rate
Pressure drop is reported both as a total over your entered length and as a rate per 100 m, since the rate makes it easy to compare across pipe sizes and runs of different lengths. Most Canadian hydronic designs target somewhere between 1 and 4 kPa per 100 m for branch piping, though this is a guideline rather than a hard limit, and many designers prioritize velocity as the primary constraint with pressure drop as a secondary check. If a manufacturer's chart or pump curve reports pressure in psi or feet of head instead of kPa, the pressure converter handles that conversion directly.
Why Fitting Losses Matter Here
The length you enter should be the equivalent length of the entire run, including an allowance for every elbow, tee, and valve, not just the measured straight pipe. A run with several fittings can have a meaningfully higher actual pressure drop than its straight-line distance would suggest. Use the fitting equivalent length calculator to total fitting losses for your specific run, then add that figure to your measured pipe length before entering it here. On a system where actual performance is in question, a field reading logged through the test, adjust, and balance calculator can confirm whether real-world pressure drop matches this calculated estimate.
Where This Result Goes Next
Once you have pressure drop for each segment of a circuit, the next step is totaling them across the full index circuit on the pump head calculator, then selecting a circulator on the pump sizing calculator that meets both the total head and flow requirement.
A Note on Accuracy
This calculator uses published nominal pipe dimensions and the standard Hazen-Williams method for estimating purposes. Actual pressure drop varies with fitting count, water temperature, and pipe age. For permit-stamped mechanical drawings or large commercial systems, confirm sizing against the current CSA B214 installation code for hydronic heating systems, registered with the Standards Council of Canada, and have a mechanical engineer verify the final design.
Frequently Asked Questions
Most Canadian hydronic designs target somewhere between 1 and 4 kPa per metre of pipe length, though the right number depends on the project. Lower values reduce pump energy cost over the system's life but require larger, more expensive pipe. Higher values save on pipe and fitting cost but increase pump head and energy use. Many designers use velocity as the primary sizing constraint and treat pressure drop as a secondary check.
Yes. The length you enter into this calculator should be the equivalent length of the run, which includes an allowance for elbows, tees, and valves, not just the measured straight pipe length. Skipping fitting losses on a run with several turns or valves can significantly understate the actual pressure drop. Use the fitting equivalent length calculator to total fitting losses, then add that to your measured pipe length before entering it here.
The pipe sizing calculator works backward from a target velocity to recommend a pipe size. This calculator works forward from a pipe size you already have in mind to check the resulting pressure drop and velocity. They use the same underlying Hazen-Williams method, so the results stay consistent whichever direction you start from.
Manufacturer friction loss charts sometimes use a different roughness coefficient, water temperature assumption, or pipe dimension standard than the generic values used here. Small differences of this kind are normal and usually do not change a sizing decision. For a project where the manufacturer's specific chart is available, that chart should take precedence over a general calculator for final design.
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