magnet formulas

B is the magnetic field, in teslas, at any point on the axis of a current loop. The direction of the field is perpendicular to the plane of the loop.

μ_o is the permeability constant (1.26x10^-6 H/m)

i is the current in the wire, in amperes.

r is the radius of the current loop, in meters.

x is the distance, on axis, from the center of the current loop to the location where the magnetic field is calculated, in meters.

Note that this is equivalent to the expression for on-axis magnetic field due to a magnetic dipole:

where A is the area of the current loop, or πr²