Hydraulic Calculator

Type in the textbox the known information. Leave only one field open in each formula and click the “calculate” button for the result of that field. The “reset” button will clear all fields. On the conversion table type in the textbox the units you want to convert.

Pump Flow or Displacement

$$GPM(Flow) = \frac{RPM * DISPLACEMENT (Cu. In./Rev.)}{231}$$

Pump Input Horsepower

$$HP(Power) = \frac{PSI(Pressure) * GPM(Flow))}{1714 * \text{% }Pump\text{ } Efficiency }$$


$$Lb-in (Torque) =\frac{PSI (Pressure) * cu.in. / rev. (Displacement)}{2π} $$


$$Lb-in (Torque) =\frac{HP(Power) *63025}{RPM} $$

Cylinder Piston Area-Blind End (Extension)

$$in^2(Area) = in (Piston\text{ } Diameter) ^ 2 * (\frac{π}{4})$$

Cylinder Piston Area-Rod End (Retraction)

$$in^2 (Area) = (in (Piston Diameter))^2 *(\frac{π}{4}) – (in(Rod Diam.))^2 *(\frac{π}{4})$$

Cylinder Force

$$lbf. (Pounds\text{ }of\text{ }Force) = PSI (Pressure) * sq. in. (Area)$$

Cylinder Flow Rate and Velocity

$$GPM (Flow) = \frac{in.^2 (Area) * in. (Stroke Travel) * 60 }{sec (Time) * 231}$$

Cylinder Volume

$$Gal (Volume)=\frac{in.^2 (Piston Area) * in. (Stroke)}{231}$$

Pressure Loss Per Foot of Pipe (Laminar Flow Only)

$$PSI/ft(Pressure Loss)=\frac{SSU(Viscosity\text{ at }Oper. Temp.) * GMP}{18300*(in(I.D. of Pipe))^4}$$

Velocity of Oil Flow in a Pipe

$$ft/sec(Velocity)=\frac{GPM (Flow)*0.3208}{(in(I.D. of Pipe))^2*0.7854}$$

Reservoir Cooling Capacity (Steel w/ Adequate Air Circulation)

BTU/hr(Heat Loss) =2*sq. ft. (Surface Area of Reservoir) * (°F (Reservoir Wall Temp.)-°F (Air Temp.))

Heat in a Hydraulic System From Unused Flow / Pressure

BTU/hr (Heat) = GPM (Flow)*1.485 *PSIG (Pressure Drop)

Heat in a Hydraulic System (Hydraulic Oil)

BTU/hr (Heat Loss) = 210 * GPM (Flow) * (°F (Return Fluid Temp.) -°F (Pump Fluid Temp.))

Heat Required to Reach a Desired Temperature

$$kWh (Heat)=\frac{Lbs. of Hyd Oil*Specific Heat*(°F (End Temp.)-°F (Beg. Temp.))}{3413}$$

Accumulator Make Up Oil Necessary to Stroke Cyl in “X” seconds

Blind End

$$Oil Req. = \frac{3.14 * Cyl. Bore Dia.^2 * Stroke}{4}-\frac{GPM * 231 * Req. Stroke}{60}$$

Rod End

$$Oil Req. = \frac{3.14*(Cyl. Bore Dia.^2-RodDia.^2)}{4}* Stroke-\frac{GPM * 231 * Req. Stroke}{60}$$

Accumulator Sizing

$$StoredOil = \frac{0.95 * Pre\text{-}charge * Vol.Size}{Min. PSI} – \frac{0.95*Pre\text{-}charge*Vol.Size}{System PSI}$$

Stored Oil if Accumulator Size is Larger

Due to heating and cooling of the nitrogen during operation, a 5% allowance has been added to the formula. Allow enough extra capacity for contingencies.







Viscosity (100° F)


Heat/ Energy


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