Piping
Equivalent Length Calculator
The equivalent length method converts a fitting K-value to an equivalent length of straight pipe that would produce the same friction head loss. This is an approximate engineering method using the relationship K = f × Le/D. Both the K-value and Darcy friction factor must be supplied by the user.
TypeInteractive calculator — separate from unit conversions
Calculator
Le output unit:
Result
Equivalent length (Le)6.75 m
Le/D ratio45
Formulas
Equivalent length from K
Le = K × D / f
Equivalent length ratio
Le/D = K / f
K from equivalent length
K = f × Le / D
Diagram
Worked example
K = 0.9, f = 0.020, D = 150 mm. Calculate equivalent length.
- 01Le/D = K / f = 0.9 / 0.020 = 45
- 02Le = K × D / f = 0.9 × 0.15 / 0.020 = 6.75 m
Result
Equivalent length is 6.75 m. Le/D ratio is 45.
FAQ
Does this look up fitting K-values?
No. You must supply the K-value. For K-values of specific fittings, consult Crane TP-410 or your fitting manufacturer's data.
Does this calculate friction factor?
No. You must supply the Darcy friction factor. Use the separate Friction Factor calculator if you need to estimate f.
Does this select pipe schedule or material?
No. You must supply the internal diameter directly. No pipe schedule or material lookup is performed.
Is the equivalent length method exact?
No. It is an approximation that assumes the friction factor in the fitting equals the friction factor in the straight pipe. This is a standard engineering simplification but introduces some error.