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Pipe Design Calculator
Straight-pipe friction (Darcy–Weisbach) with optional fitting losses (K). Namespaced, responsive, printable.
| Material | Diameter (mm) | Length (mm) | Flow (L/s) | Fitting Type | Qty | Row Loss (m) | Actions |
|---|---|---|---|---|---|---|---|
| Overall Pipe Loss: | 0.000 | ||||||
Custom Fitting Coefficients (Global Overrides)
Leave blank to use defaults. Select None – Straight Pipe (K=0) or turn on Straight‑Pipe Mode to ignore fittings entirely.
Quick Tips
- For straight pipe only, pick None – Straight Pipe (K=0) or enable Straight‑Pipe Mode.
- Target ~1–2 m/s velocities for typical water services to balance noise and loss.
- Darcy–Weisbach used for pipe friction; fittings via K·V²/2g. Equivalent length (Le) shown per row.
- Add another row to represent a change in material/diameter/flow segment.
How This Pipe Design Calculator Works
A clear, step‑by‑step look at the math under the hood — Darcy–Weisbach for straight pipe, optional K‑factor losses for fittings, and the Swamee–Jain explicit correlation for turbulent friction factor.
Quick Overview
The calculator computes head loss per segment and in total. Each row uses the Darcy–Weisbach equation for straight pipe and (optionally) adds local losses from fittings/valves using K‑factors.
Assumptions & Constants
- Fluid: water at ~20 °C → ρ = 998 kg/m³, ν = 1.0×10⁻⁶ m²/s
- Gravity g = 9.81 m/s²
- Pipe roughness (ε): PVC 1.5e‑6 m, Copper 1.5e‑6 m, Steel 45e‑6 m, GI 150e‑6 m
- Friction factor f: laminar (Re < 2300) → f = 64/Re; otherwise Swamee–Jain explicit formulation
The Core Math (with definitions)
What about equivalent length (Le)?
K and Le are linked: K = f · (Le/D). Since f depends on Re and ε/D, Le changes with flow/diameter. That’s why the tool takes K as the input and only displays Le for context.
What Happens When You Click “Calculate”
One‑Row Demo (matches the main calculator)
Use the same math as the tool for a single row. Try switching GI ↔ PVC to see roughness effects on f and head loss.
Worked Example (validates the formula)
Inputs: GI pipe, D = 75 mm, L = 10 m, Q = 11 L/s, K = 0.
- A = π(D/2)² = 0.004418 m² → V = Q/A = 2.489 m/s
- Re = V·D/ν ≈ 1.87×10⁵ (turbulent)
- ε/D = 0.00015 / 0.075 = 0.002 → Swamee–Jain → f ≈ 0.0246
- hpipe = f (L/D) V²/(2g) = 0.0246 × 133.33 × 0.3158 = 1.034 m
Matches the main calculator to three decimals.
Compare with Hazen–Williams (straight‑pipe only)
Hazen–Williams (HW) is handy for water in the fully rough turbulent regime. It’s an empirical formula; we include it here only for comparison. It does not support fittings directly.
Use the main calculator for design (it handles fittings and different flow regimes); rely on HW for quick sense checks only.
Features That Help You Design Faster
- Straight‑Pipe Mode: Hides fitting columns and forces K=0 for all rows.
- Global K overrides: Enter your own K values once; rows use them unless a row is set to a custom K.
- Details panel: Per‑row V, Re, f, pipe vs fittings head, and equivalent length (derived).
- CSV export & local save: Download every row; your work auto‑saves in your browser.
Accuracy & Limitations
- For laminar (Re < 2300), f = 64/Re is exact for fully developed flow in circular pipe.
- For transitional (≈ 2300–4000), expect uncertainty; real systems can deviate.
- Roughness varies with age, scale, or lining. Adjust ε (or pick Custom) if your system differs.
- K values are typical. Prefer manufacturer data where available.
Keep Learning
Ideas to Make Readers Stay Longer
- Add a toggle to flag rows when V > 2.5 m/s or Re < 2300 (laminar) — quick QA.
- Offer a preset gallery (fire main, chilled water, domestic cold) that loads realistic defaults.
- Provide a unit helper (mm ↔ inch, L/s ↔ gpm) that writes into inputs.
- Collect email to send the CSV + a short guide on choosing K and equivalent lengths.
