How fast is Mach 20 really?

Assassination classroom quickly became a fan favourite where students have to kill their teacher. Who has never thought of that at least once? Anyway, the act of killing their teacher is ridiculously difficult for many reasons, one of them being that he can move at Mach 20.


Yea I also numbly accepted the whole vague Mach 20-speed aspect just believing that it must be fast. Just I never knew how fast until I did some digging. So how fast is Mach 20 really? Turns out the anime and manga were not exaggerating as that is really, really fast as in not even our rockets that break the Earth’s atmosphere go that fast.

Let me break it down for ya, Mach is the ratio of the speed of an object to the speed of sound. It is usually used in fluid dynamics. So Mach 2 is twice the speed of sound. So already by going at Mach 20, Koro-sensei is going 20 times the speed of sound. The speed of sound is measured in various ways but for this, I shall stick to terms of distance. The speed of sound travels at 1234.8 Km per hour. So putting Mach 20 into plain numbers and distance we get:

20 X 1234.8 Km per hour = 24 696Km per hour

That is 411km per minute, so almost 6,850km per second!

I drive about 18km to work every day and that takes me 15-20 minutes. If I could drive at Mach 20 I would be at work in under 3 seconds. So basically in just one hour, he could travel halfway around the earth and in 2 hours he could have gone around the world completely, so much for 80 days.

So yeah, Mach 20 is insanely fast. What do you think of Koro-sensei being able to travel at Mach 20? I think it is mind-boggling. Even simplifying it as I have, it is still hard to wrap my head around.  This is another reason I like anime, it gets the brain working and you end up learning something new.


12 thoughts on “How fast is Mach 20 really?

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  1. sound travels at roughly 1000 feet per second. actually, 1125 feet per second, but 1000 is pretty close. So mach 20 is 20 thousand feet per second, or about 6000 meters per second. 6 kilometers per second. so 3 seconds to go 18 kilometers. If sound goes 411 km in one minute, how can it possibly go a longer distance than that in less time? 6000 kilometers per second is 2% of the speed of light. check your math, folks. 411 divided by 60 is not larger than 411.


    1. The math is correct, the comma in (6,85 km per s) does not mean six thousand. In South Africa a comma is used to differentiate between the decimal point. I had my math checked before posting.


      1. No it is 6.86 km per second, or 6,869 meters per second lol so not THAT fast but still REALLY fast


    1. In South Africa we use a comma to split decimal point, some countries use the comma to split the thousand and the proceeding 3 significant figure intervals. 🙂


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