Pick a fitting, enter the fluid and flow, then press Calculate to see the resistance coefficient K from each of the three industry methods side-by-side.
Crane: K = (L/D)·fT
Hooper 2-K: K = K₁/Re + K∞(1 + 1/Dᵢₙ)
Darby 3-K: K = K₁/Re + Kᵢ(1 + K_d/D_nom^0.3)
When to use each method
- Crane TP-410: Industry standard. Fast and conservative. Best for turbulent flow (Re > 10,000) and quick estimates. May underpredict at low Re.
- Hooper 2-K: Adds Reynolds correction. Good balance of accuracy and simplicity. Better for laminar and transitional flow.
- Darby 3-K: Most accurate. Accounts for Re and size scaling. Use for critical calculations.
Recommended values
- Which method: 3K (Darby) for the widest size/Re range; 2K (Hooper) for moderate; Crane K = f·(L/D) for fully turbulent.
- Size effect: K drops as diameter grows — always use the size-corrected value, not a single textbook K.
- Sum then convert: Add all fitting K, then ΔP = K·ρ·v²/2; combine with straight-run friction for total loss.
- Entrance/exit: Sharp entrance K ≈ 0.5, exit K ≈ 1.0 — easy to forget on suction lines.
Limitations
- Isolated fittings: K values assume each fitting is standalone; close-coupled fittings interact and are not simply additive.
- Single-phase: No cavitation, flashing, or two-phase multipliers — liquid or gas turbulent flow only.
About the standards
- Crane TP-410: Flow of Fluids.
- Hooper 2-K: Method for minor losses.
- Darby 3-K: Method for minor losses.