Magnetic Field Calculator (Biot–Savart & Ampère)

Magnetic flux density of a long wire, circular loop, solenoid or toroid.

How to use the Magnetic Field Calculator

Enter or select: Source, Current I, Distance / radius r, Axial distance x, Number of turns N, Solenoid length ℓ.
The results (Flux density B, Field strength H) are calculated instantly as you type.
Use “Copy link” to share the calculation with the same input values.

Formula

Wire: B = μ₀I/(2πr)
Loop centre: B = μ₀NI/(2r)
Loop axis: B = μ₀NIr²/(2(r² + x²)^(3/2))
Solenoid: B = μ₀NI/ℓ
Toroid: B = μ₀NI/(2πr)