Based on a recent (summer 2018) study, the Milky Way is around 200,000 light years across.

A light year is the distance light travels in vacuum over the course of one Earth year, equal to almost 6,000 billion miles. That conversion makes 200,000 light years difficult to imagine. To try to put it into perspective, the distance light travels in one second is roughly 8x the distance around Earth's equator (a light year is 32 million times farther than that); the distance from Earth to the sun (93 million miles) is 8 light minutes (= 0.000015 light years).

The man-made object most distant from Earth is Voyager 1, launched in 1977. In mid-2012 it left our solar system, at which point the spacecraft was at 121x the sun-Earth distance. That distance, even at 11.3 billion miles, is only 0.002 light years.