What's the difference between MMF and magnetic field strength?

MMF (A·t) is the total driving force around a magnetic circuit—like total voltage. Magnetic field strength H (A/m) is MMF per unit length—like voltage gradient. For a uniform field: H = MMF / length. H is distributed; MMF is the integrated total.

How does MMF relate to electromagnet strength?

Higher MMF creates more magnetic flux, making stronger electromagnets. But actual flux depends on the magnetic circuit: Φ = MMF / Reluctance. Iron cores dramatically reduce reluctance (increase permeability), so the same MMF produces much more flux than with air cores.

Why use many turns instead of high current?

Power loss = I²R, so high current causes heat. Many turns of thin wire achieve the same MMF with lower current and losses. Trade-off: more turns means more wire resistance, larger size, and higher inductance. Design optimizes for the specific application.

Magnetomotive Force Converter

About Magnetomotive Force Conversion

Magnetomotive force (MMF) is the driving force that establishes magnetic flux in a magnetic circuit—analogous to voltage (EMF) in an electric circuit. Just as voltage drives current through electrical resistance, MMF drives magnetic flux through magnetic reluctance. It's produced by current flowing through conductor turns: MMF = N × I, where N is the number of turns and I is current. Doubling either turns or current doubles the MMF, giving designers flexibility in electromagnet and transformer design.

The SI unit is the ampere-turn (A·t) or simply ampere (A) when turns are implicit in the magnetic circuit analysis. The older CGS unit gilbert (Gb) is still encountered in some permanent magnet specifications and older literature. MMF is fundamental to designing transformers (where primary MMF balances secondary MMF), inductors (where MMF creates stored magnetic energy), motors (where MMF from stator and rotor interact), and electromagnets (where MMF determines lifting force). The magnetic circuit equation Φ = MMF/ℜ parallels Ohm's law.

Our converter handles all standard magnetomotive force units used in electromagnetic device design.

Common Magnetomotive Force Conversions

From	To	Multiply By
A·t	Gb (gilbert)	1.257 (4π/10)
Gb	A·t	0.7958 (10/4π)
A·t	kA·t	0.001
kA·t	A·t	1,000
A·t	mA·t	1,000
Gb	mGb	1,000
mA·t	A·t	0.001
A·t	mA·t	1,000

Magnetomotive Force Unit Reference

Ampere-turn (A·t) – The SI unit of magnetomotive force. One turn of wire carrying one ampere of current produces 1 A·t of MMF. A 500-turn coil at 2 A produces 1000 A·t—the same as a 100-turn coil at 10 A. In magnetic circuit analysis, "ampere" alone often refers to ampere-turns when the number of turns is specified separately. Typical values: small relay 50-500 A·t, solenoid valve 500-2000 A·t, lifting electromagnet 10,000+ A·t.

Gilbert (Gb) – The CGS unit of magnetomotive force, named after William Gilbert (1544-1603), author of "De Magnete" and pioneer of magnetism research. 1 Gb = 10/(4π) A·t ≈ 0.7958 A·t, or conversely 1 A·t ≈ 1.257 Gb. The gilbert is still occasionally encountered in older technical literature and some permanent magnet specifications.

Kiloampere-turn (kA·t) – 1000 ampere-turns, used for large electromagnets and industrial applications. Heavy-duty lifting magnets for scrap yards may require 10-50 kA·t. Large MRI magnets use superconducting coils with millions of ampere-turns. Electric arc furnace transformers operate at hundreds of kA·t.

Milliampere-turn (mA·t) – 0.001 A·t, used for very small magnetic circuits like miniature relays, read/write heads, and MEMS magnetic devices. Precision magnetic sensors often operate in this range.

Milligbert (mGb) – 0.001 Gb ≈ 0.796 mA·t. Occasionally used in older literature for small magnetic devices.