Electric Machines

Electric machine calculators and formulas for motors, generators, and rotating machinery relationships. Includes motor torque, slip, and generator EMF calculations.

11Formulas

All levels Difficulty

Updated Jul 2026

← All Electrical Engineering (151) Electric Machines (11)

Fundamental

Motor Full-Load Current (Three Phase)

I = P / (√3 × V × cos θ × η)

Fundamental

Motor Full-Load Current (Single Phase)

I = P / (V × cos θ × η)

Fundamental

Watts to Horsepower Conversion

HP = P(W) / 746

Fundamental

Horsepower to Watts Conversion

P(W) = HP × 746

Fundamental

Armature Current of a DC Motor

I_a = (V − E_b) / R_a

Fundamental

Generator EMF Equation

E = 4.44·f·N·Φ

Fundamental

Motor Efficiency

η = P_out / P_in

Fundamental

Torque of a DC Motor

T = k·Φ·I_a

Fundamental

Back EMF of a DC Motor

E_b = V − I_a·R_a

Fundamental

Slip of an Induction Motor

s = (N_s − N_r) / N_s

Fundamental

Synchronous Speed

N_s = 120·f / P