K-Factor to Equivalent Length: Worked Example

1. Calculator Inputs

Select the units below before entering the numbers. These are fixed benchmark inputs for checking the calculator.

2. Step-by-step Math

Equate the two head-loss expressions

Fitting loss: hL = K V² / (2g)
Straight-pipe loss: hL = f (Le/D) V² / (2g)
K = f Le/D
Le = KD/f

Both coefficients must use the same reference velocity. This cancellation is not valid if one K is based on a different pipe area.

Convert diameter and calculate length

D = 2.067 / 12 ≈ 0.172 ft
Le = 5 × 0.17225 / 0.02
Le = 43.0625 ft ≈ 13.1 m

Use the Darcy friction factor. A Fanning factor of 0.005 corresponds to Darcy f = 0.02; entering 0.005 directly would produce four times the correct equivalent length.

Reverse the calculation

K = f Le/D
K = 0.02 × 43.0625 / 0.17225 = 5

Select K from equivalent length, enter 43.0625 ft, and retain the same bore and Darcy friction factor.

3. Compare Your Answers

Keep full precision during the calculation. The calculator may display fewer digits; compare answers rounded to three significant figures; retain unrounded intermediate values.

Second check

At the same K and diameter, changing Darcy f from 0.02 to 0.025 reduces equivalent length to 34.45 ft. The specified K has not changed; the straight pipe now dissipates more energy per foot.

4. Assumptions and Method

K = 5 and f = 0.02 are supplied benchmark values, not recommended values for a named fitting. Equivalent length depends on friction factor and reference diameter. Do not count both this equivalent length and the original K in the same pressure-loss total.

Equation definitions and implementation: K-Factor to Equivalent Length Calculator. See also calculation methodology and other worked examples.