Calculator Inputs
Use SI units. For sizing, enter allowable head loss. Minor losses are handled with a total K value.
Example Data Table
Use these sample values to validate your setup quickly.
| Case | L (m) | D (m) | Q (m³/s) | K (—) | ε (m) | ρ (kg/m³) | μ (Pa·s) |
|---|---|---|---|---|---|---|---|
| Site water line | 60 | 0.15 | 0.02 | 2.5 | 0.000045 | 998.2 | 0.001002 |
| Drainage header | 120 | 0.30 | 0.06 | 3.0 | 0.00026 | 998.2 | 0.001002 |
| Pump discharge | 40 | 0.10 | 0.01 | 6.0 | 0.000045 | 1025 | 0.00108 |
Formula Used
The calculator applies the Darcy–Weisbach relation for major losses and a K-based method for minor losses.
Velocity: \( V = \dfrac{Q}{A} \) and \( A=\dfrac{\pi D^2}{4} \)
Reynolds number: \( Re=\dfrac{\rho V D}{\mu} \)
Major head loss: \( h_f=f\dfrac{L}{D}\dfrac{V^2}{2g} \)
Minor head loss: \( h_m=K\dfrac{V^2}{2g} \)
Total head loss: \( h=h_f+h_m \) and \( \Delta P=\rho g h \)
Friction factor uses laminar \(f=64/Re\). For turbulent flow, you can select Colebrook-White or explicit approximations.
How to Use This Calculator
- Pick a calculation mode: head loss, required diameter, or maximum flow.
- Enter pipe length, diameter, and flow as applicable for the mode.
- Add a total K value for fittings and entries, if known.
- Select a roughness preset or enter ε directly for your pipe material.
- Choose a fluid preset or input density and viscosity manually.
- Click Calculate to display results above the form.
- Use the CSV or PDF buttons to export your latest run.
For construction submittals, document assumptions: pipe ID, lining condition, temperature, and how K was assembled.
Darcy–Weisbach Design Notes
1) What the calculator reports
The tool computes major and minor head losses and converts them to pressure drop. Head loss is shown in meters of fluid, and ΔP is shown in kPa, bar, and psi. The pump head line adds elevation change to friction head for quick checks. Export results for QA notes and field records.
2) Typical construction data
Many site water, bypass, and drainage systems target velocities near 1–3 m/s. Laminar flow is generally below Re ≈ 2300, but most water services are turbulent. Representative roughness values include new steel ε ≈ 0.000045 m, rusted steel ε ≈ 0.00026 m, and PVC ε ≈ 0.0000015 m.
3) Fittings and minor losses
Minor losses use a total K multiplied by the velocity head, \(V^2/(2g)\). Build K by summing entrances, elbows, tees, valves, reducers, and exits from handbooks or manufacturer data. Compact skid piping often falls in the K = 2–10 range, while long runs are usually dominated by the major term. Avoid double counting by using either K values or equivalent lengths, not both.
4) Worked example values
For L = 60 m, D = 0.15 m, and Q = 0.02 m³/s (20 L/s), area is about 0.0177 m² and velocity is about 1.13 m/s. With water near 20°C (ρ ≈ 998 kg/m³, μ ≈ 0.001 Pa·s), Reynolds number is roughly 170,000, so the friction factor is evaluated using the selected turbulent method plus roughness and diameter.
5) Using the sizing modes
Diameter sizing finds the smallest diameter that keeps total head loss at or below your allowable value. Flow sizing finds the highest flow that still meets the head-loss limit. For submittals, record pipe ID, temperature, lining condition, and how K was assembled. Add a reasonable design margin for fouling and future demand.
FAQs
1) What is the difference between head loss and pressure drop?
Head loss is energy loss expressed as meters of fluid. Pressure drop is the same loss expressed as pressure, computed as ΔP = ρ g h. Both describe the same friction effect.
2) Which friction factor method should I choose?
Use Colebrook-White when you want a robust reference calculation. Haaland and Swamee–Jain are fast explicit options that usually match closely for turbulent water services.
3) How do I estimate the total K value?
Add K for each fitting: entrance, elbows, tees, valves, reducers, and exit. Manufacturer data, handbooks, or project specs provide K values. Enter the sum as a single number.
4) Does the tool handle laminar flow?
Yes. If Reynolds number is below about 2300, the calculator uses f = 64/Re. This is most relevant for very small pipes, viscous fluids, or low flows.
5) Should I use internal diameter or nominal size?
Use internal diameter. Nominal size can differ from actual ID due to schedule, lining, or wall thickness. Using the correct ID improves velocity, Reynolds number, and head-loss accuracy.
6) Why does roughness matter?
Roughness affects the turbulent friction factor. Older or rusted pipes increase ε, raising head loss for the same flow. Smooth pipes like PVC typically reduce losses and pumping demand.
7) Can I use this for pump selection?
It is suitable for preliminary pump head estimates when combined with elevation change. For final selection, include all system components, check operating points, and verify with project specifications.