Friction Loss Calculator
Calculate friction loss per 100 feet of hose or pipe using the Hazen-Williams formula — the standard method used in fire service hydraulics and plumbing system design.
Fill in the required fields to see your result.
Use this calculator on your website
Add this free Friction Loss Calculator to your blog, article, or business website. Copy the embed code and publish it in minutes.
Perfect for blogs, WordPress, Webflow, and business websites.
This is the friction loss in psi per 100 feet of pipe or hose at the given flow rate. Multiply by (actual length / 100) for total friction loss over your run.
Need a calculator like this?
Calciro can build a custom calculator around your formulas, pricing rules, or lead-generation process.
How Friction Loss in Pipes Is Calculated
Friction loss estimates the pressure drop water experiences flowing through a pipe or hose, based on flow rate, pipe diameter, and pipe material (via a roughness/C-factor).
How Friction Loss Is Calculated
The calculator above uses the Hazen-Williams formula, relating flow rate, pipe diameter, and the pipe material's C-factor to pressure loss per unit length — see the calculator for your exact figures, since results depend heavily on your specific flow rate and pipe parameters.
What Affects Friction Loss?
Higher flow rates increase friction loss significantly (the relationship isn't linear). Smaller pipe diameters dramatically increase friction loss for the same flow. Rougher pipe materials (lower C-factor) increase loss compared to smoother materials (higher C-factor).
Common Friction Loss Calculation Mistakes
Using the wrong C-factor for pipe material and age — older, corroded pipes have significantly rougher interior surfaces than new pipe of the same material. Confusing friction loss per 100 feet with total friction loss over the actual pipe run length. Ignoring fitting losses (elbows, valves, reducers), which add to straight-pipe friction loss in a real system.
How to Use This Calculator
Enter the flow rate in GPM, the pipe or hose diameter in inches, and the Hazen-Williams C-factor (roughness coefficient — 120 is a common default for average condition pipe).
Formula & Methodology
Hazen-Williams formula: Friction Loss (psi per 100 ft) = 4.52 × Q^1.85 / (C^1.85 × d^4.87), where Q is flow in GPM, C is the roughness coefficient, and d is inside diameter in inches.
Example: 150 GPM through 2.5" hose, C=120
FL = 4.52 × 150^1.85 × 100 / (120^1.85 × 2.5^4.87) ≈ 7.9 psi per 100 ft.
The Hazen-Williams C-factor varies significantly by pipe material, age, and condition — using the wrong C-factor can meaningfully skew results. This calculates loss per 100 ft only; multiply by your actual length ratio for total loss.
For planning and estimation purposes. Verify against your department's or engineer's standard hydraulic references for critical fire-flow or system design decisions.
Related Calculators
- Equivalent Nodal Loads CalculatorCalculate the consistent local nodal-force vector for a two-node Euler–Bernoulli beam under a linearly varying transverse load.
- Target Heart Rate CalculatorCalculate your target heart rate training zone from your age.
- Tank Volume CalculatorCalculate cylindrical tank volume in gallons from diameter and height measurements.
- Amps to kW CalculatorConvert amps to kilowatts for single-phase and three-phase electrical loads.
- Bending Angle CalculatorCalculate sheet metal bend allowance from bend angle, inside radius, thickness, and K-factor.
- Boiler Feed Pump CalculatorSize a boiler feed pump's capacity from steam output and a safety factor.
Related Guides
- How Friction Loss Is Calculated in Pipes: Hazen-Williams and Darcy-WeisbachLearn how friction loss in pipes is calculated using the Hazen-Williams and Darcy-Weisbach equations. Covers C factors, Reynolds number, and pressure drop for fire suppression and plumbing systems.
- How to Size a Boiler Feed Pump: Flow Rate, Head & Power ExplainedSize a boiler feed pump by calculating required flow rate, total head, and motor power. Covers the sizing formulas, net positive suction head (NPSH) requirements, and efficiency factors.
- How to Convert Amps to Kilowatts: Single-Phase and Three-Phase FormulasConvert amps to kilowatts using the correct formula for single-phase or three-phase circuits. Covers power factor, worked examples, and a quick reference table.
- How to Calculate Tank Volume Step by Step: Cylinders, Rectangles, and ConesCalculate tank volume using the correct formula for your tank shape — cylindrical, rectangular, horizontal cylinder, or cone. Includes unit conversion and partial fill calculations.
- How to Calculate Sky Background ElectronsConvert sky surface brightness in mag/arcsec² to electron rate per pixel, aperture counts, and background noise.
Frequently Asked Questions
- What is the Hazen-Williams formula used for?
- It's the standard formula for calculating friction loss in water flowing through pipes and fire hose, widely used in fire service hydraulics and plumbing design.
- What C-factor should I use?
- 120 is a common default for average-condition pipe. New PVC can be 150+, while old, corroded steel pipe can be 100 or lower — use your pipe's actual rated or measured C-factor when known.
- Is this loss for my whole pipe run?
- No — the result is friction loss per 100 feet. Multiply by (your total length ÷ 100) to get total friction loss for your run.
Last updated 7/12/2026