Flywheel Energy Calculator
Calculate the kinetic energy stored in a solid-disc flywheel from its mass, radius, and rotational speed.
How it works
- 1Enter the flywheel mass, outer radius, and rotational speed in your preferred unit system.
- 2The calculator models the flywheel as a solid disc and computes the moment of inertia I = ½·m·r².
- 3Stored kinetic energy E = ½·I·ω² is shown in kJ or BTU alongside the moment of inertia in kg·m².
Use cases
- Sizing flywheels for uninterruptible power supplies (UPS) and energy storage systems.
- Evaluating engine flywheel designs for smoothing torque pulses in automotive applications.
- Estimating energy recovery potential in regenerative braking and industrial press machines.
Frequently asked questions
What formula does this calculator use?
For a solid disc, I = ½·m·r². Kinetic energy is E = ½·I·ω², where ω = 2π·n/60 rad/s and n is speed in rpm. At 50 kg, 0.3 m radius, 3000 rpm: I = 2.25 kg·m², E ≈ 111 kJ.
Why does doubling the rpm quadruple the stored energy?
Energy depends on ω², so if you double the rotational speed, ω doubles and ω² quadruples — the stored energy increases by a factor of four.
Does this apply to a hollow ring flywheel?
No — this tool models a solid disc (I = ½·m·r²). A thin ring has I = m·r², storing twice as much energy for the same mass and radius.
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