The number of wraps in a pickup's coil is one of the primary factors that determines its electrical resistance. As more wraps are added to the coil, the length of the wire increases, and thus the resistance increases.
The relationship between the number of wraps and resistance is not linear, however. The rate at which the resistance increases will slow down as more wraps are added. This is because the wire used in pickup coils is typically very thin, and the resistance of a thin wire increases less quickly than that of a thick wire.
As a general rule of thumb, doubling the number of wraps in a pickup coil will increase its electrical resistance by about 4 times. Therefore, if a pickup has a resistance of 100 ohms with 1,000 wraps, doubling the number of wraps to 2,000 will increase the resistance to about 400 ohms.
The resistance of a pickup can also be affected by other factors, such as the type of wire used, the diameter of the wire, and the winding pattern. However, the number of wraps is the primary factor that determines the resistance of a guitar pickup.