Enter the total number of turns or conductors and the current into the calculator to determine the magnetomotive force.

Magnetomotive Force Formula

The following equation is used to calculate the Magnetomotive Force.

mmF = I * N 
  • Where mmF is the magnetomotive force (ampere-turns)
  • I is the current (amps)
  • N is the number of turns or conductors

To calculate the Magnetomotive Force, multiply the current by the number of turns.

What is a Magnetomotive Force?


Magnetomotive force (MMF) is the property that drives currents in coils and causes them to produce a magnetic field.

The MMF value depends on three variables: the number of turns in the coil, the current flowing through it, and its geometric construction (such as whether it has multiple coils or layers).

How to Calculate Magnetomotive Force?

Example Problem:

The following example outlines the steps and information needed to calculate the Magnetomotive Force.

First, determine the current of the system. In this example, the current is 400 amps.

Next, determine the number of turns in the coil. For this problem, the number of turns is 5.

Finally, calculate the magnetomotive force using the formula above:

mmF = I * N

mmF = 400 * 5

mmF = 2,000 ampere-turns


What is the significance of the number of turns in a coil for magnetomotive force?

The number of turns in a coil directly influences the magnetomotive force (MMF). The more turns a coil has, the greater its ability to produce a magnetic field when a current flows through it. This is because MMF is calculated as the product of the current (I) and the number of turns (N), indicating that both factors are crucial for determining the strength of the magnetic field generated.

Can magnetomotive force be negative?

Magnetomotive force (MMF) itself is a scalar quantity and is typically considered positive in the context of its definition, which involves the absolute values of current and the number of turns. However, the direction of MMF can be conceptually negative if considering the direction of current flow in a coil and its effect on the direction of the magnetic field produced, following the right-hand rule. In practical terms, MMF is positive, but the direction of the magnetic field it generates can be reversed by reversing the current’s direction.

How does the geometric construction of a coil affect its magnetomotive force?

The geometric construction of a coil, including its shape, size, and whether it has multiple layers or coils, can significantly affect its magnetomotive force (MMF). The overall effectiveness of a coil in generating a magnetic field is not only a function of the current and the number of turns but also how these turns are spatially arranged. Coils with compact turns and multiple layers can produce stronger magnetic fields due to the cumulative effect of the magnetic fields from each turn being in close proximity, enhancing the overall MMF.