Gauss units are used to measure the strength of magnets. One gauss unit is equivalent to about twice the average strength of the earth’s magnetic field. The strength of a magnet depends on its size and thickness. Therapeutic magnets use from 200 to 1500 gauss, which is only a fraction of what an MRI machine would emit. Every magnetic device has a manufacturer’s gauss rating, though the actual strength of the magnet at the skin’s surface is often much less than this number.