What is the top speed of the Flash?

The information provided in this answer isn't really correct on Barry's top speed. As far as I'm aware, and I watched the show up to season 6, Barry's top speed was revealed in Season 4, Episode 15, called "Enter Flashtime".

In this episode, a nuclear bomb is detonated, and all of Barry's friends are in the site of the nuclear explosion. So in order to save everyone, Barry got so fast, he was able to hold multiple conversations with other characters, walk sort of casually, and run to "charge up" then throw a lightning bolt, all while the nuclear bomb was, well, blowing up. He also left the site of the explosion, went to Star Labs to talk to Iris, and did some other things.

According to the YouTube Channel "Comic Books vs. The World", his speed was around 99.9999% the speed of light:

After a lot of research, I found out Barry's top speed.

In S6, Gideon tells Barry that ultraviolet light travels at a speed of 186,000 miles/second, and that the current Barry is 80 times slower than that, so we can do the math and check it out:

186,000 miles/sec/80 = 2,325 miles/sec (Barry's top speed)

This converts to:

2,325 miles/s = 8,370,000 miles/hr = 13,470,209 km/h = 3,741,724 m/s = Mach 10,909