It is made a comparison of functions approximating the main magnetization curve of electrical steels, selected according to two main criteria: obtaining the simplest expressions in an analytical study and achieving a minimum calculation error in quantitative calculations of devices with ferromagnetic components. The cases are considered when ferromagnetic elements in devices operate at alternating current and at high values of magnetic induction, that is, they are in a mode close to saturation, while the phenomena of hysteresis are usually neglected, and the main magnetization curve is used as the magnetic characteristic of the ferromagnetic element, it is shown, that when the devices operate in a saturated mode, an incomplete polynomial of n - degree can be used for these purposes. It is proved that the errors when approximating by polynomials with degrees 9 and 11 give the smallest errors not exceeding 12 and 8% for components of devices based on cold-rolled steels, and errors not exceeding 13% when approximating by polynomials with degrees 3 and 5 for components of devices based on hot-rolled steels.