Faraday's Law Calculator. Faraday's Law states that a changing magnetic field through a coil induces a voltage — the Faraday's Law Calculator quantifies exactly how much. Enter your coil's Number of Turns, Magnetic Flux Change (ΔΦ), and Time Change (Δt) — with your preferred flux and time units — to calculate the Induced EMF in volts, along with its magnitude, millivolt equivalent, and converted flux and time values. Also try the Helical Coil Calculator.
Faraday's Law states that a changing magnetic flux through a closed circuit induces an electromotive force (EMF) in that circuit. The magnitude of the induced EMF is proportional to the rate of change of magnetic flux. Mathematically: EMF = −N × (ΔΦ / Δt), where N is the number of turns, ΔΦ is the change in flux, and Δt is the time interval. See also our calculate Electromagnetic Force (Lorentz) Total Lorentz Force.
The negative sign reflects Lenz's Law, which states that the induced EMF always acts in a direction that opposes the change in magnetic flux that caused it. This is a consequence of energy conservation — the induced current creates a magnetic field that resists the original flux change.
Magnetic flux (Φ) measures the total magnetic field passing through a given area. It equals the product of the magnetic field strength (B) and the area (A) perpendicular to it: Φ = B × A. The SI unit of magnetic flux is the Weber (Wb), where 1 Wb = 1 T·m².
The induced EMF is directly proportional to the number of turns (N) in the coil. Doubling the number of turns doubles the induced EMF for the same rate of flux change. This is why transformer coils and generators use many turns to amplify the voltage output.
This calculator supports Weber (Wb), Milliweber (mWb), Microweber (µWb), and µT·m² as flux units. The tool automatically converts your input to Webers before computing the EMF, so you can enter values in whichever unit is most convenient for your application.
Faraday's Law is the operating principle behind electric generators, transformers, induction motors, MRI machines, wireless charging systems, and induction cooktops. Any device that converts mechanical motion or changing magnetic fields into electrical energy relies on this law.
If the magnetic field B changes uniformly over an area A, the flux change is ΔΦ = ΔB × A. Substitute this into Faraday's formula: EMF = −N × (ΔB × A) / Δt. You can pre-calculate ΔΦ in Webers and enter it directly into this calculator along with the corresponding time interval.
EMF (electromotive force) is the energy provided per unit charge by a source — it represents the 'driving force' that pushes current through a circuit. Voltage (or potential difference) refers to the energy difference between two points in a circuit. In an ideal circuit with no internal resistance, the induced EMF equals the terminal voltage. You might also find our Skin Depth Calculator useful.