What is the approximate diameter of the observable universe?

The observable universe has an approximate diameter of 93 billion light-years.

That figure is larger than the universe’s age in light-years because space itself has expanded while light was traveling toward us. The universe is about 13.8 billion years old, but the most distant matter whose ancient light can reach Earth today is now roughly 46 billion light-years away in every direction. Doubling that radius gives the commonly quoted diameter of about 93 billion light-years.

The observable universe is not necessarily the entire universe. It is the region from which light or other signals have had time to reach Earth since the hot, dense early universe. Beyond its boundary, there may be much more space and matter, but those regions are currently unobservable from Earth.

A common mix-up is to answer 13.8 billion light-years. That number combines the universe’s age with the speed of light and ignores cosmic expansion; the diameter estimate accounts for the changing scale of space.