Calculate the missing value for reference dynamic pressure, loss coefficient, or total pressure drop using any two known inputs in psi, kPa, bar, or Pa.
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Loss Coefficient Formula
The loss coefficient is the unitless ratio of dissipative total-pressure loss to reference dynamic pressure q = ฯvยฒ/2. For steady incompressible flow, q is total minus static pressure at the reference location. Use the velocity reference associated with the coefficient; an arbitrary static-pressure drop is not q. Choose a quantity to solve, then enter the other two values.
- K = loss coefficient, unitless
- ฮPt = dissipative total-pressure loss
- ฮP = reference dynamic pressure q (total minus static pressure at the reference location for incompressible flow)
To calculate the loss coefficient, the calculator divides total pressure drop by the reference dynamic pressure.
To calculate the total pressure drop, it multiplies the reference dynamic pressure by the loss coefficient.
To calculate the reference dynamic pressure, it divides the total pressure drop by the loss coefficient.
Pressure values can be entered in psi, kPa, bar, or Pa. The calculator converts pressure units internally before applying the formula.
Pressure Unit Conversions Used
These rounded conversion factors are useful when checking by hand. The calculator uses one factor for each unit and its reciprocal, with Pa as the common base unit.
| Unit | To psi | From psi |
|---|---|---|
| psi | 1 psi = 1 psi | 1 psi = 1 psi |
| kPa | 1 kPa = 0.145038 psi | 1 psi = 6.89476 kPa |
| bar | 1 bar = 14.5038 psi | 1 psi = 0.0689476 bar |
| Pa | 1 Pa = 0.000145038 psi | 1 psi = 6894.76 Pa |
Example Problems
Example 1: Find the loss coefficient
You have a total pressure drop of 12 psi and a reference dynamic pressure of 4 psi.
The loss coefficient is 3.
Example 2: Find the total pressure drop
You have a reference dynamic pressure of 25 kPa and a loss coefficient of 2.4.
The total pressure drop is 60 kPa.
FAQ
Is the loss coefficient unitless?
Yes. The loss coefficient is unitless because it is a ratio of two pressure values. The pressure units cancel out as long as both pressure values are converted to the same unit before division.
Why do the pressure values need matching units?
The formula compares one pressure value to another. If one value is in psi and the other is in kPa, the ratio will be wrong unless you convert them first. The calculator handles this conversion automatically.
Can the loss coefficient be zero?
Zero K gives zero pressure loss for a specified reference pressure. Zero K and zero loss do not determine a unique reference dynamic pressure; positive loss with zero K is incompatible. Similarly, a zero reference pressure cannot determine K by division.
