Formula:
BHP = Q × P / (C × n)
Where:
BHP = Brake Horsepower in horsepower
Q = Flow Rate in gallons per minute
P = Pressure in pounds per square inch
n = Efficiency expressed as a decimal
C = A conversion factor depending on units of flow and pressure
| Units | Value of C |
| GPM / PSI | 1714 |
| GPM / Hd. Ft. | 3960 / SG |
| Barrels per Day / PSI | 58773 |
| Barrels per Day / Hd. Ft. | 135788 / SG |
| CFM / PSI | 229.16 |
| CFM / Hd. Ft. | 529.45 / SG |
| Cubic Meters per Hour / PSI | 6.4875 |
| Cubic Meters per Hour / Hd. Ft. | 14.989 / SG |
* SG = Specific Gravity of the fluid
Horsepower [HP] = Flow Rate [GPM] × Pressure [PSI] / (C × Efficiency)
Example #1:
Flow Rate = 750 GPM
Pressure = 125 PSI
Efficiency = 78%
Calculate: 750 [GPM] × 125 [PSI] / (1714 × 0.78) = 70.12 HP
Example #2:
Flow Rate = 125,000 BBL/Day
Pressure = 798 Hd.Ft.
SG = 0.75
Efficiency = 81%
Calculate: 125,000 [BBL/Day] × 798 [Hd.Ft.] / {( 135,788 / 0.75) × 0.81} = 680.2 HP
Note: The calculation above is only for single acting plunger and piston pumps. In a double acting plunger pump, the flow rate should be multiplied by 2. In a double acting piston pump, a modified piston diameter should be used where DP = 2 × DPiston – DRod
Where:
DPiston = Diameter of the Piston in inches
DRod = Diameter of the Drive Rod connecting to the piston
