The second derivative of the axial magnetic flux density is found to vanish for an electromagnet composed of three circular coaxial coils if the spacing between adjacent coils is a, if each coil contains equal ampere turns, if the radii of the end coils are a, and if the radius of the center coil is ∼5a/4. Consequently, this tri‐coil electromagnet produces a relatively constant axial magnetic flux density within its length of 2a. Comparisons are made to the Helmholtz coil.