Helmholtz Coil Calculator

Calculate the magnetic field at the center of a Helmholtz coil pair, or determine the current needed to cancel an ambient field.

A Helmholtz pair consists of two identical circular coils separated by a distance equal to their radius, a geometry that produces an exceptionally uniform magnetic field at the midpoint. The on-axis field is given by B = (4/5)^(3/2) × µ₀NI/R, where N is the number of turns per coil, I is the current, and R is the coil radius. This calculator operates in two modes: forward mode computes the field strength in T, mT, µT, and Gauss from N, I, and R; cancel mode inverts the formula to find the current needed to null an ambient field such as Earth's field (25–65 µT). Use cancel mode when shielding a magnetically sensitive experiment or sensor from environmental interference.

Input
Field at Center
B
0.0001499T
B
0.1499mT
B
149.86μT
B
1.4986G
Abridged Optics — Helmholtz Coil Calculator v1.0B = (4/5)^(3/2) × μ₀NI/R. Valid at the midpoint between two coils separated by distance R.

All information, equations, and calculations have been compiled and verified to the best of our ability. For mission-critical applications, we recommend independent verification of all values. If you find an error, please let us know.