Moment of Inertia Converter

Convert mass moment of inertia between kg·m², g·cm², lb·ft², lb·in², slug·ft², and oz·in² for rotational dynamics and machinery calculations.

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Moment of inertia converter Convert positive mass moment of inertia between SI, CGS, and imperial units for rotational dynamics, flywheels, drivetrains, and machinery data sheets.

Mass moment of inertia

Common presets

Mass moment, not area moment

This converter handles mass moment of inertia used in rotational dynamics. It does not convert second moment of area values used for beam bending and section properties.

Rotational property only

This page converts the inertia value only. It does not calculate torque, angular acceleration, flywheel energy, or geometry-based inertia from mass distribution.

Enter a mass moment of inertia Provide a non-negative inertia value to compare the supported unit systems.

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Rotational Dynamics

Moment of inertia converter: kg·m², g·cm², slug·ft², and mass-inertia units explained

A moment of inertia converter rewrites the same mass moment of inertia in the unit your mechanics notes, machinery documentation, or rotational model expects. This quantity appears in flywheel, drivetrain, rotor, and rigid-body problems, and it is easy to confuse with unrelated section-property units unless the quantity is named clearly.

About this calculator

Reviewed March 2026

Methodology

Converts the source unit into kilogram square metres as the shared SI base, then derives the supported SI, CGS, and imperial mass-moment-of-inertia outputs from that same rotational property.

Limitations

Translates mass moment of inertia only and does not convert area moment of inertia or section properties
Treats the input as a non-negative rotational property magnitude
Keeps imperial entries mass-based rather than force-based
Formatting rounds displayed values for readability

Disclaimer

Use this converter for unit translation only. For flywheel design, drivetrain sizing, structural analysis, or safety decisions, confirm the correct inertia quantity and engineering model separately.

Sources

Engineering LibreTexts — Mass Moment of Inertia — Engineering reference explaining mass moment of inertia and its common unit families.
NASA — Moment of Inertia classroom connection — NASA public educational resource using kg·m² for moment of inertia.
NIST Guide to the SI, Appendix B.9 — NIST source for the official mass and length factors used to derive the supported inertia units.

See our calculation methodology and editorial standards for how this estimate is produced.

What mass moment of inertia measures

Mass moment of inertia describes how strongly a body resists angular acceleration about a chosen axis. It depends on both total mass and how far that mass sits from the rotation axis.

That is why the quantity is expressed as mass times length squared, such as kg·m², g·cm², or slug·ft². Changing the unit does not change the physical distribution being described.

I = Σ m r²

Shows the discrete form linking inertia to mass distribution about an axis.

τ = I α

Connects torque, mass moment of inertia, and angular acceleration in rigid-body rotation.

1 kg·m² = 10,000,000 g·cm²

Links the common SI and CGS mass-inertia scales used in engineering tables.

Do not confuse this with area moment of inertia

Mass moment of inertia is a dynamics quantity for rotating bodies. Area moment of inertia, also called second moment of area, is a structural section property used in beam bending and stiffness calculations.

The names are similar enough to cause mistakes, so this page is explicit about converting mass-based rotational inertia only.

Why imperial labels need care

Imperial mechanics references may use pound-mass, slug, and ounce-based inertia expressions. Those are mass-based units and should not be confused with pound-force or torque units such as lbf·ft.

This converter keeps the quantity strictly in mass-times-length-squared form so rotational property tables, machine data, and mechanics exercises stay internally consistent.

Moment of Inertia Converter

Moment of inertia converter: kg·m², g·cm², slug·ft², and mass-inertia units explained

What mass moment of inertia measures

Do not confuse this with area moment of inertia

Why imperial labels need care

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