What formula does this calculator use?

Kinetic energy E = ½Iω², where I is the moment of inertia in kg·m² and ω is angular velocity in rad/s. RPM is converted via ω = 2π × RPM / 60.

What is the moment of inertia for a solid disk?

For a solid disk: I = ½MR². For a hollow cylinder (thick-walled): I = ½M(R_outer² + R_inner²). For a thin ring: I = MR².

Can I enter moment of inertia directly?

Yes. Select "Custom I" to enter the moment of inertia in kg·m² directly, bypassing the shape presets.

How does angular velocity relate to RPM?

ω (rad/s) = 2π × RPM / 60. At 3000 RPM, ω ≈ 314.16 rad/s.

Why does a heavier rim store more energy than a solid disk of equal mass?

Mass concentrated at a larger radius increases I proportionally to R². Moving mass outward raises the moment of inertia and therefore stored energy, even at the same total mass and speed.

Flywheel Energy Calculator

Calculate kinetic energy stored in a flywheel from its moment of inertia and angular velocity, with shape presets and unit conversion.

Flywheel Parameters

Shape / Inertia mode

Mass

Outer radius

Rotational speed

Enter parameters and click Calculate

Summary

The Flywheel Energy Calculator computes the kinetic energy stored in a rotating flywheel using E = ½Iω². Enter your flywheel geometry (or moment of inertia directly), set the rotational speed, and get the stored energy in Joules, watt-hours, or BTU. Shape presets automatically calculate I for solid disks, hollow cylinders, and thin rings from mass and radius. All computation runs in your browser.

How it works

Select a shape preset (solid disk, hollow cylinder, thin ring) or enter the moment of inertia directly.
For shape presets, enter mass in kg (or lb) and the required radius values.
Enter the rotational speed in RPM or rad/s.
Click Calculate to see stored energy in Joules, watt-hours, and BTU.
Adjust any field and recalculate instantly.

Use cases

Sizing flywheels for energy storage systems and UPS devices.
Estimating kinetic energy in rotating machinery for safety analysis.
Designing flywheel-based regenerative braking systems.
Verifying stored energy in engine crankshafts and industrial press flywheels.
Educational demonstrations of rotational kinetic energy.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu