Hydraulic Calculators: Flow, Force, Torque & Pressure Tools

FPD's calculator suite covers eight core hydraulic calculations: pump power and flow, cylinder force and speed, gear pump displacement, weight conversion, motor torque and power (including gearbox winch line pull), pressure conversion, power conversion, and torque conversion. All calculators are free to use and run instantly in your browser, no login or download required!

Pump drive power (kW) is calculated as system pressure (bar) multiplied by flow rate (l/min), divided by 600 times pump efficiency. Enter pressure, pump displacement (cc/rev), input speed (rpm), and efficiency (%), and the calculator returns both the required power (kW) and the resulting flow (l/min). This is the standard formula used to size an electric motor or engine to drive a hydraulic pump.

Cylinder force is calculated from system pressure acting on the piston area — full bore area for extend force, and bore area minus rod area (annular area) for retract force. Enter bore diameter, rod diameter, stroke length, pressure, flow rate, and mechanism efficiency, and the calculator returns extend and retract force (in kN and tonnes), stroke time, rod speed, and exhaust flow for both directions.

Gear pump displacement is calculated from the gear geometry: outside root diameter, inner root diameter, and gear height. Enter these three measurements and the calculator returns the pump's displacement, which determines its flow output at a given input speed.

Enter a value in either the kg or lb field and the calculator converts it instantly using the standard factor of 1 kg = 2.20462 lb. This is commonly used when cross-referencing component weights between NZ/metric and imported US-spec parts documentation.

Motor torque (Nm) is calculated from motor displacement (cc/rev) and the pressure drop across the motor (bar), adjusted for mechanical efficiency. Enter motor displacement, input flow, motor efficiency, and pressure drop, and the calculator returns output speed (rpm), power (kW), and torque (Nm), the key figures for matching a motor to a winch, drive, or rotating load.

Winch line pull and speed are derived from the motor's output torque and speed combined with the gearbox ratio and drum diameter. Enter the gearbox ratio, bare and full drum diameters, and speed, and the calculator returns torque, line pull (in tonnes), and line speed (m/min) for both a bare drum and a full drum — line pull is highest and line speed lowest when the drum is bare, and this reverses as the drum fills.

Enter a pressure value in any one of PSI, bar, kg/cm², or kPa, and the calculator converts it to the other three using standard conversion factors (1 bar = 14.5038 psi = 1.01972 kgf/cm² = 100 kPa). This is useful when working across equipment specified in different regional pressure units.

Enter a value in either HP or kW and the calculator converts it using the standard factor of 1 kW = 1.34102 HP. This is commonly needed when comparing NZ/European kW-rated equipment against US/imported HP-rated specifications.