Disclaimer: Potentially minor story spoilers ahead for Assassination Classroom.

Another disclaimer: I’m not good with math and science. I’ve tried these calculations because they seemed fun to punch out, and I’m well aware that I may be wrong.

Last disclaimer I promise: All screenshots taken from Kissanime.com

screancap1One of the first things that we learn about this yellow blobby octopus monster is that he can travel at speeds of up to Mach 20. It’s a term that is thrown around a lot by the cast of the show, and it’s often used as one his greatest feats.

Though, thinking logically, how did Karasuma get this exact number? It’s incredibly specific, and I doubt that Koro-Sensei would be cooperative enough to let the military measure his top speed. He’s dodged assaults and missiles, but never under a scientific and measurable environment, so we have to assume that Karasuma’s “Mach 20” is just an estimate.

But let’s look closer at the show and examine Koro-Sensei’s speed, and see if it’s REALLY in Mach 20.

First of all, what does “Mach 20” even mean?

The term “Mach” typically applies to planes, and it refers to the multiple of the speed of sound at which the plane is going through in a certain medium. In layman’s terms, Mach 1 is the speed of sound, Mach 2 is twice the speed of sound, and so on. Physicians will go on about the impact of a medium on the Mach, but I’m not a physician, I’m an idiot. This is a rough editorial on the speed of a fictional yellow octopus, not a physics paper on jet planes at mach speed.

So Mach 20 is twenty times the speed of sound. How fast is that?

The speed of sound is 340.29m/s. Multiply this value by twenty, and we get Koro-Sensei’s estimated speed according to the military: 6805.8m/s. In other words, 6.8km per second.

Of course, that’s just a number, let’s put it into more understandable terms. Travelling at top speed:

      • Koro-Sensei can sprint the length of 62 full-size NFL Football fields in one second
      • Koro-Sensei can circle the earth in 1 hour and 44 minutes if he were to do so squarely on the equator line
      • Koro-Sensei can travel from Japan to Korea in just over 2 minutes (138.97 seconds)

That is, though, according to the estimate of the military. Koro-Sensei himself has admitted that this is around his top speed, but the reliability of his word is uncertain at best and sketchy at worst.

Of course, there are some feats of Koro-Sensei that cannot really be measured or quantified due to the nature of the show and manga. Feats like changing an entire room into new year festivities, including the clothes of the students, in seconds. Feats like picking up spilt soup in midair with an eyedropper, and adding sugar to balance it out its taste. Feats like making afterimages for each student to help them revise for the upcoming midterms. It’s simply not really all that possible to measure how fast he is with these kinds of accomplishments. All that we can gather from this is that Koro-Sensei is very, very, VERY fast. But how fast?


To us slow humans, we really can’t tell the difference between Mach-1, Mach-2 and Mach-20. We just see it as “very fast”. Similarly, we can easily tell the difference between 10 lions and 1,000 lions, but by the time it gets to 1,000,000 lions or 1,000,000,000 lions, we just register the number as “a lot”. So the instantaneous sprints that render Koro-Sensei invisible in seconds may seem like a ridiculously unquantifiable speed to us humans, it may not be so for Koro-Sensei.

Thus, it’s not really all that easy or possible to quantify Koro-Sensei’s speed in terms we can really understand.

I’m still going to try though, it looks fun.

So let’s look deeper into Koro Sensei’s two biggest measurable feats and let’s see if this estimate is really all that realistic.


Travelling from Japan to Hawaii in “the space of one lecture” – Koro-Sensei’s leisurely speed.

Early in the show, Koro-Sensei took Nagisa and Karma to Hawaii in order to watch a new movie release. They simply hopped right into Koro Sensei’s coat and blasted off into the sky, arriving in Hawaii in what seemed like a short amount of time. Koro-Sensei gave a lecture as they were flying, and it ended right as they landed, which leads Nagisa to appropriately comment “We made it all the way to Hawaii in the space of one lecture!”


Kunugigaoka is a school situated in Tokyo in Assassination Classroom’s fictional world mirroring our own, so one of the easiest ways to scale Koro Sensei’s feats is with a real life equivalent. A trip from Tokyo to Hawaii, on a relatively straight line with a distance of 6,485km on a Boeing 777 travelling at 917kmph would take 7 hours and 19 mins.

Fast, but clearly, Koro-Sensei took MUCH less time.

A lecture in an average Japanese Junior High School is around 50 mins. So, scaling Koro Sensei’s speed to that of a Boeing 777’s puts his speed at

8,051kmph, or,  2.24 km per second. This is Mach 6. It’s not quite Mach 20, but we need to assume the following:

      • Koro-Sensei probably could not go at his full speed while carrying Nagisa and Karma. This is in terms of both Koro-Sensei having to carry the weight of both students, as well as the idea that he must care for both students. Nagisa and Karma landed in Hawaii with no signs of discomfort. (which shouldn’t even be possible when considering that they just flew 6 times the speed of sound, but maybe that’s a post for another day)
      • Koro-Sensei probably could not go at his full speed while giving a lecture
      • Koro-Sensei was not fatigued in the slightest


So this is Koro Sensei’s leisurely dash. He was not even phased and was severely handicapped, and yet he could outspeed a commercial plane several times over. This is honestly no joke, and he outdid himself in these long distance sprints more than once.

Remember – to Nagisa and Karma, it must have felt like they were going at speeds too fast to even comprehend. In their eyes, Mach-6 and Mach-20 aren’t ALL that different because they’ve never really been able to compare those speeds to something they can relate to.

But this is Koro-Sensei at his most relaxed, carrying students and giving lectures in midair as if it were second nature. We need a sprint of ONLY him, in a time where speed really matters. Thankfully, such a scenario does exist.

Travelling from Rio De Janerio to Japan “extremely quickly” – Koro-Sensei in a hurry

Similar to the previous feat of Koro-sensei travelling from Japan to Hawaii, Koro-sensei travelled a global distance in a time that commercial planes would only dream of. However, some things are different this time around. After the class was lured and captured by the Reaper, Koro-Sensei sensed something slightly wrong when he was unable to contact every single member of the group. In a hurry, he blasted off from Brazil to Tokyo to meet up with Karasuma to engage the Reaper and rescue the students. A few things are different this time:

      • Rio de Janerio is much, much farther away from Tokyo compared to Hawaii (6,485km vs 18,559km)
      • Karma and Nagisa were not present to weigh Koro-Sensei down
      • Karma and Nagisa were not present to consciously impact Koro-Sensei’s speed (out of consideration for their health).
      • There is a sense of urgency, as in Koro-Sensei’s own words “I’ve got a bad feeling about this”


A normal Boeing 777 would take 20 hours and 44 mins to arrive in Rio De Janerio from Tokyo, assuming that it travels 917kmph at all times. This is basically a day flight. Now, let’s compare a Boeing 777’s time to Koro-Sensei’s time.

Assuming that the episode happens in real time (Koro-Sensei failed to contact the group right before they engaged in combat with the reaper at 15 minutes into the episode), we can use the episode time to draw assumptions on how quickly it took Koro-Sensei to get back from Rio.


The Reaper and Irina knocks out all the students in 4 minutes 45 seconds, to which there is an unspecified short time jump to the students all conscious in their prison cell.

In terms of real life experience, a powerful punch from a boxer can knock someone out for 5 minutes on the extreme, long end of things. Considering that the Reaper’s power should stay somewhere between reasonable human levels (he’s not Goku or Saitama by any stretch of the imagination), and the shock absorber P.E uniforms that the students have, we can make a highball estimate of their knocked-out time. Let’s assume that the students black out and then regain consciousness in 20 minutes, which is already an extremely generous estimate. When the students are seen awake in the following scene, it takes no more than 20 seconds for the Reaper to realise that Karasuma and Koro-Sensei are outside their lair.


Let’s be clear: in this calculation, we are assuming that

      • Koro-Sensei started flying the moment the calls failed
      • The students were knocked out by the Reaper in the same amount of time that the show depicted (On screen, the fight ended in 4m45s)
      • The gap of time that is seen between Itona’s unconditional surrender and the scene with all of the students together was 20 minutes.

Remember, the entire incident with the Reaper only took place over the course of a single day, and the students woke up for school the next day, walking in without any serious injuries or broken bones. As sad as it is for his reputation, the Reaper did not do any permanent damage to any of these students – and with that, we can already assume that a time gap of 20 minutes between their re-capture and their latter scene is already an incredibly generous estimate.

So now we can craft a timeline between Koro-Sensei’s calls all the way to Koro-Sensei’s arrival, all in the assumed timestamps that we’ve made up. All of these valuables are assumptions, so there’s an extremely high degree of inaccuracy (who knows, the Reaper may have knocked them out for two hours for all that’s possible in fiction), but let’s go with the values that we have made up for now. Here’s the timeline.

Koro-Sensei calls the group and fails.  -> The Reaper knocks out the group ( 4m45s) ->The students were unconscious and then were moved to the prison, and then wake up(20m0s) -> the Reaper finds Koro-Sensei and Karasuma outside his door (0m20s)

Our total time is, therefore, 25m05s. Let’s see what this means.

Koro-Sensei dashed from Brazil to Tokyo at an average speed of 12.331km per second. That is ridiculous. How ridiculous?

That’s Mach 36.

Of course, that’s nowhere near the crazy units like the speed of light, but it’s still ridiculously fast. Much faster than the show would lead us to believe.

Now, we can even get that time even LOWER, because:

      • We didn’t account for the time it took for Koro-Sensei to let Karasuma know that the kids have been kidnapped
      • We didn’t account  for the time it took for Koro-Sensei to change into his dog costume (???)
      • We didn’t account  for the time it took for Koro-Sensei, in his dog costume, to track down the kids by scent, or any dead ends or mishaps involved in such a scenario (wtf)


Let’s slow down for a second. Just to confirm our calculations, let’s backtrack. If Koro-Sensei were travelling at his estimated maximum speed of Mach-20, how long would it take? At the Mach-20 speed of 6.8km per second, he would arrive in Tokyo in around 45m. Still incredibly fast, but the time gap seems much more unrealistic. Should the students be knocked out for this long, they surely would have suffered permanent physical or brain damage, (or at least damage that would linger for days ) which is clearly not the case.

These calculations basically hinge on the estimated time gap between Itona’s surrender and the student’s scene later. I’ve drawn on estimated real life examples and then gave it a lot of lenience assuming that the Reaper is beyond normal, but assuming that the students were knocked out any longer would mean that there’s no way they would have been able to just get up and go to school the day after. They didn’t even look like they were in all that much pain in the anti-teacher prison cell as Karasauma fought the Reaper, so the longer the estimates are, the more unlikely and unrealistic the situation is for the students.

Maybe Koro-Sensei can go faster. Maybe he was even holding back some (he wasn’t tired at all when he arrived. If anything, he was energetic in his dog suit). But for now, I shall estimate that Koro-Sensei’s maximum speed is NOT Mach-20. Instead, I propose that it may be around this value of Mach-36.

This would still put him slightly slower than the Mach-40 steroid tentacle drugged Reaper at the season finale, but much faster than the original estimates of Karasuma.


The show is a lot more focused on the impact of Koro-Sensei on these students; turning all of the E class, hopeless delinquents whose uselessness is meant to motivate the other students, into academic behemoths capable of going toe to toe with the school elites. Assassination Classroom is not a grand scheme of assassination(notice how a lot of the time, it’s painted out as blatantly obvious that their assassination attempts will fail), but instead focuses on the impact of a truly, honestly amazing teacher, and how influential a good one (or a bad one) can be in a student’s life.

Thus, the development of the characters is much more focused on the E-class instead of the teacher. Nagisa finds confidence in himself and applies his talents for assassination into a more practical and helpful career. Karma lets go of his delinquency and laziness, finding true power and enjoyment in hard work and intense academic competition. Kayano drops her façade and finds a love that motivates her to the ends of the earth. The students have grown so much from Season 1, and all of it can be attributed to Koro-sensei.

But we’ve all neglected one critical part of this – Koro-Sensei can grow as well.

It’s not obvious because his power scale is so far off compared to all of the other characters, and his personality is always spick-span perfect teacher-esque, but Koro-Sensei does indeed develop. He even says in his own beautifully orchestrated words

“I say assassination is education. The assassination classroom’s teacher will get stronger every time he teaches!”


Koro-Sensei’s top speed being at Mach 20 may have been an extremely accurate measurement of his top speed early in the series. But the incident with the reaper took place in the middle of season 2, after the academic showdown with the A class, the tentacle battle against Itona and the mini-war against Takaoka. No doubt, Koro-Sensei must have grown a significant amount during these experiences, both mentally, and possibly physically.

One issue with this theory is that Koro-Sensei did not go to space with Karma and Nagisa, and Nagisa’s monologue seems to suggest that it’s because that Koro-Sensei isn’t fast enough to reach escape velocity (the speed you need to go at to leave the atmosphere). Therefore, this calculation is totally bogus, because clearly, Koro-Sensei is able to reach it  (12.33kmp/s > 11.2km p/s (at the earth’s surface) )

The explanation that I propose is simple: He didn’t want to. Here’s why I think so:

      • He’d be retracting from the experience of his two precious students’ expedition into space
      • He’d have no way to enter the ship to gather data anyway, so going into space has no meaning
      • He may not want to enter a ship that’s’ collecting data on how to murder him
      • He doesn’t want to appear in front of the ship personnel because his presence in space could lead to new information that could endanger him, or worse, his students.
      • He may not even be able to breathe in space, and getting equipment that would allow him to do so would be too much of a hassle ( I don’t think there are tailor made space-suits for octopus monsters)


I’m not very smart, and these calculations were certainly fun to punch out. I’m aware that I may be wrong, and I’m aware that I may be totally off with my assumptions. Maybe the reaper knocked the kids out for hours. Maybe Koro-Sensei truly wasn’t fast enough to get into space. Either way, though,

This has been An Idiot’s Guide to Koro-Sensei’s speed – but hey, don’t take my word for it. I’m just some idiot.