Famiiar 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 cubiic 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 