Familiar Formula in Customary U.S. Units 

Same Formula in the New SI Standard Units 

Torque, Power, and Speed Relations in Hydraulic Pumps & Motors 

T = HP × 5,252 ÷ RPM 

T = kw × 9,543 ÷ RPM 
HP = T × RPM ÷ 5,252 
kw = T × RPM ÷ 9,543 
RPM = HP × 5,252 ÷ T 
RPM = kw × 9,543 ÷ T 

T is torque in foot lbs. 

T is torque in Nm (newton meters) 
RPM is speed in revolutions per minute 
RPM is speed in revolutions per minute 
HP is horsepower (33,000 ft. lbs/min.) 
kw is power in kilowatts 

Hydraulic Power Flowing in the System 

HP = PSI × GPM ÷ 1,714 

Kw = Bars × dm^{3} ÷ min ÷ 600 

HP is horsepower (33,000 ft. lbs. per min.) 

Kw is system power in kilowatts 
PSI is gauge pressure, lbs. per square inch 
Bars is system pressure 
GPM is flow in gallons per minute 
dm^{3}/min is flow in cubic decimeters per minute 

Force Developed by Air or Hydraulic Cylinder 

T = A × PSI 

N = A × Bars × 10 

T is force or thrust, in pounds 

N is cylinder force or thrust in newtons 
A is piston area in square inches 
A is piston area in square centimeters 
PSI is gauge pressure, lbs. per sq. in. 
Bars is gauge pressure 

Travel Speed of a Hydraulic Cylinder 

S = V ÷ A 

S = V ÷ 6A 

S is travel speed in inches per minute 

S is travel speed in meters per second 
V is volume of oil into cylinder, cu. ins. per min. 
V is oil flow in cubic decimeters per minute 
A is piston area in square inches 
A is piston area in square centimeters 

Barlow's Formula for Calculating Burst Pressure of Tubing and Pipe 

P = 2t × S ÷ O 

P = 2t × S ÷ O 

P is burst pressure in PSI 

P is burst pressure in bars 
t is wall thickness of pipe in inches 
t is wall thickness of pipe in millimeters 
S is tensile strength of pipe material in PSI 
S is tensile strength of pipe material in bars 
O is outside diameter of pipe in inches 
O is outside diameter of pipe in millimeters 

Velocity of Oil flow in Hydraulic Lines 

V = GPM × 0.3208 ÷ A 

V = dm^{3}/min ÷ 6A 

V is velocity in feet per second 

V is oil velocity in meters per second 
GPM is oil flow in gallons per minute 
dm^{3}/min is flow in cubic decimeters per second 
A is inside area of pipe in square inches 
A is inside area of pipe in square centimeters 

Recommended Maximum Oil Velocity in Hydraulic Lines 

Pump suction lines  2 to 4 per sec. 

Pump suction lines  0.6 to 1.2 m/s (meters/sec) 
Pressure lines up to 500 PSI  10 to 15 ft/sec. 
Pressure lines up to 35 bar  3.0 to 4.5 m/s 
Pressure lines 500 to 3,000 PSI  15 to 20 ft/sec. 
Pressure lines 35 to 200 bar  4.5 to 6.0 m/s 
Pressure lines over 3,000 PSI  25 ft/sec. 
Pressure lines over 200 bar  7.5 m/s 
Oil lines in air/oil system  4 feet per sec. 
Oil lines in air/oil system  1.2 m/s 

See Design Data Sheet 25 for many other conversions between U.S. customary and ISO units 