Equivalent Length Calculator (K-Factor)

Units System

Pipe Material

Nominal Pipe Size

Pipe Schedule

Straight Pipe Length (for info) m

Used only to report "effective length".

Friction Factor Mode

Darcy Friction Factor (f)

Typical turbulent f ≈ 0.018–0.025.

Enter a list of fittings with their K-factor and quantity. Total K = Σ (K × Quantity); Equivalent length Leq = (Total K × D) / f.

Fitting Description	K-Factor	Quantity	Action

Pipe Internal Diameter: -

Roughness / Diameter (ε/D): -

Friction Factor (f) Used: -

Total K-Factor (ΣK): -

Equivalent Length (Leq): -

Straight + Equivalent Length: -

ΣK: Total minor-loss coefficient, Σ(K_i × Qty_i) (dimensionless).
D: Pipe internal diameter (m). Calculated from pipe database as ID = OD − 2×WT.
ε: Absolute roughness (m) from selected material.
ε/D: Relative roughness (dimensionless).
Re: Reynolds number (dimensionless), used for friction factor when selected.
f: Darcy–Weisbach friction factor (dimensionless).
L_eq: Equivalent length representing fitting losses as an equivalent straight-pipe length (m).
L_eff: Effective length = L_straight + L_eq (m).

Total K: ΣK = Σ(K × Qty)
Equivalent length method: based on Darcy–Weisbach loss forms, L_eq = (ΣK × D) / f
Friction factor (if from Re): Haaland explicit approximation (turbulent/transition), with laminar fallback:
- Laminar: f = 64 / Re (Re < 2300)
- Haaland: 1/√f = −1.8 log10[( (ε/D)/3.7 )^1.11 + 6.9/Re]
Unit handling: Internal calculations are in SI (m). If Imperial is selected, input straight length (ft) is converted to m for computation, and results are reported in both m and ft.

This tool supports the common K-factor (minor-loss) approach and converts it to an equivalent length for use in pressure-drop calculations.
K values are user inputs. Use reputable sources (e.g., Crane Technical Paper 410) or vendor data for valves/fittings.
Pipe OD and wall thickness are based on standard dimension tables (e.g., ASME B36.10M for carbon/alloy steel and ASME B36.19M for stainless). Always confirm against your project piping spec.
Haaland provides an explicit approximation to Colebrook; for detailed hydraulic design you may prefer a full Colebrook solver and a validated roughness model.
Validity: Ensure the selected f (or Re-based f) is consistent with your flow regime and that the same diameter basis is used as in your system model.

Equivalent Length Calculator