An electromagnetic wave is a form of energy that consists of both electric and magnetic fields oscillating together. It does not have a physical size in the same way that a solid object does. Rather, it extends indefinitely in space, propagating outward from its source.
However, it's worth noting that the size of an electromagnetic wave can be described in terms of its wavelength. The wavelength represents the distance between two consecutive points in the wave that are in phase (e.g., two crests or two troughs). This measurement is commonly used to characterize electromagnetic waves.
In summary, while an electromagnetic wave does not have a physical size from one end to the other, its size can be quantified by its wavelength, which represents the spatial extent between corresponding points in the wave.