Plan pipe sizing with quick friction loss checks. Choose material C values and units easily. See headloss, velocity, and pressure drop in seconds below.
| System | Length | Diameter | C | Flow | Typical output (head loss) |
|---|---|---|---|---|---|
| Metric | 150 m | 150 mm | 150 | 25 L/s | ≈ 5.2 m |
| US | 500 ft | 6 in | 140 | 500 gpm | ≈ 17 ft |
| Metric | 80 m | 100 mm | 120 | 10 L/s | ≈ 4.7 m |
The Hazen-Williams relationship estimates friction head loss for pressurized water flow:
When solving for flow, the equation is rearranged to compute Q from a target head loss. Velocity is computed from Q/A, and pressure drop is approximated from ρ·g·hf.
Use this calculator to size water distribution lines, temporary bypass piping, and commissioning loops where pressurized, full pipe flow is expected. The Hazen‑Williams method is empirical and most reliable for clean water at normal temperatures. It supports quick comparisons between pipe options during estimating, procurement, and construction sequencing, before detailed network modeling is completed. Apply it early to shortlist diameters for bids and submittals.
Enter the actual inside diameter, not nominal size, because fittings, liners, and wall thickness change hydraulic capacity. Choose a realistic C value for the installed material condition; new smooth plastics are higher, while older iron or tuberculated lines are lower. The tool converts all inputs internally, so mixed units still produce consistent results. Confirm lengths include risers, headers, and any permanent offsets.
Head loss represents energy required to overcome friction along the straight run. Compare the calculated head loss against available pump head or supply pressure, then reserve margin for minor losses from bends, valves, and meters. Pressure drop is shown as an approximate equivalent to help coordination with pump curves and pressure ratings on site. For long runs, review headloss gradient to spot bottlenecks.
Velocity helps confirm acceptable scouring risk, noise, and erosion at outlets. In construction work, very high velocity may indicate water hammer sensitivity and may require staged valve operation, surge control, or larger diameter pipe. Very low velocity can increase sediment deposition; adjust diameter or operational flow to stay within project criteria. Keep velocities within limits for flushing and disinfection.
Record the assumptions used for length, diameter, and C value, and attach the exported report to shop drawings or method statements. During installation, verify pipe ID, coating type, and cleanliness before pressure testing. After commissioning, compare measured pressures and flows with calculated expectations to validate the hydraulic path. Update calculations when as‑built routing differs from the plan.
C is a roughness coefficient that reflects internal pipe condition. Higher C means smoother pipe and lower friction loss. Use project specifications or published reference values, and reduce C for aging, scaling, or biofilm expected in service.
It is intended for water in pressurized, full pipes near normal temperatures. For other fluids, slurries, or significant temperature changes, use Darcy‑Weisbach with appropriate friction factors and fluid properties.
No. The calculation covers straight-pipe friction only. Add minor losses using K factors or equivalent length for elbows, tees, valves, meters, and reducers, then sum them with the straight-run head loss.
Enter inside diameter. Nominal sizes vary by schedule, lining, and manufacturer, which can change capacity and velocity. If you only have nominal size, convert it to an estimated inside diameter from the pipe data sheet.
Acceptable velocity depends on owner criteria, noise, erosion, and surge risk. Many projects target moderate velocities and avoid extreme values. Use the velocity output to decide if a larger diameter, lower flow, or surge control is needed.
Differences can come from unaccounted fittings, elevation changes, partially closed valves, debris, or incorrect diameter and C assumptions. Verify the installed routing, measure actual flow, and recalibrate inputs to match commissioning data.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.