What is the formula for rotational kinetic energy?

Rotational kinetic energy is one half times moment of inertia times angular speed squared: I.

Can I use RPM directly?

RPM must first be converted to radians per second: pi.

Different shapes place mass at different distances from the axis, so they have different moments of inertia even with the same mass and radius.

Calculate rotational kinetic energy from moment of inertia and angular speed, solve inverse values and compare common rotating shapes.

Calculate

Body shape

Shape factor 0.4

Mass, kg

Radius, m

Angular velocity

Angular velocity unit

English SERP intent centers on the formula for a rotating rigid body and quick conversion between RPM and angular speed.

K_{rot} = \frac{1}{2} I ω^{2}

I is moment of inertia and omega is angular speed in radians per second.

ω = \frac{2 π R P M}{60}

RPM must be converted before it is used in the energy formula.

K_{rot} = \frac{L ^{2}}{2 I}

Energy can also be expressed from angular momentum about the same axis.

Moment of inertia comes first

For complex or off-axis parts, calculate or measure moment of inertia first, then use it here.

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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