What is the formula for Magnetomotive Force (MMF)?

The Magnetomotive Force (MMF) formula is F = N × I (ampere-turns), where F—Magnetomotive force (ampere-turns); N—Number of coil turns; I—Coil current (A).

What does F mean in the Magnetomotive Force (MMF) formula?

F is Magnetomotive force (ampere-turns).

Magnetomotive Force (MMF)

Q: How do you calculate Magnetomotive Force (MMF)?

Use the formula F = N × I (ampere-turns). Magnetomotive force is the magnetic-circuit analogue of voltage: it is the "drive" that pushes magnetic flux around a core, produced by a coil of N turns carrying current I. Enter the values you know in the calculator above and it solves for the remaining variable.

F = N × I

Calculator

MMF

Number of Turns

Current

Result

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Formula

F = N × I (ampere-turns)

Description

Magnetomotive force is the magnetic-circuit analogue of voltage: it is the "drive" that pushes magnetic flux around a core, produced by a coil of N turns carrying current I. Doubling either the turns or the current doubles the MMF and therefore the flux for a given reluctance. It is the source term in the magnetic Ohm’s law.

Variables

F — Magnetomotive force (ampere-turns)
N — Number of coil turns
I — Coil current (A)

Practical Notes

MMF drives flux through reluctance just as EMF drives current through resistance: Φ = F / S. Increasing turns raises MMF without raising current, which is why electromagnets use many turns.

Related Concepts

All Magnetics & Transformers formulas →

Transformer EMF Equation Transformer VA Rating Transformer Voltage Regulation Transformer Current Ratio Transformer Copper Loss Transformer Iron (Core) Loss Transformer Turns-per-Volt Transformer Impedance Matching

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