Flywheel Sizing Calculator

About this calculator

A flywheel stores rotational kinetic energy in a spinning mass to smooth out fluctuations in mechanical power delivery — the energy stored is E = ½·I·ω², where I is the moment of inertia and ω is the angular velocity. This calculator works backward from a target energy to store and an operating angular velocity to find the required moment of inertia (I = 2E/ω²), then uses the solid-disk formula I = ½·m·r² (rearranged to mass = 2I/r²) to find the mass needed at a given radius.

Mechanical and automotive engineers size flywheels for uses like smoothing the power pulses in a piston engine between combustion strokes, storing energy in kinetic energy recovery systems (KERS), and stabilizing punch presses and other machinery that draws power in short, heavy bursts — sizing the disk correctly means balancing enough stored energy against the added mass and rotational inertia the rest of the system has to support.