I OFFICIALLY HAVE PROOF THAT DEKU IS FASTER THAN SOUND
Ignore the numbers; I won't be using them.
Anyways, this picture is from the movie, My Hero Academia: Two Heroes.
Unlike DBZ's massive canon problem, this one perfectly integrates into the anime.
This is before Deku changed his fighting style to kicks, so he's still at five percent of One For All.
That gun looks like a sniper; so I'll guess that's what it is. I mean, the shooter is looking through a scope.
Rifle bullets range from 2600-3400 feet per second, or 800-1000 meters per second for those on the metric system. I'll guess the bullet hasn't decreased in speed much since Deku is being shot from POINT BLANK.
Anyways, I'll underestimate and guess that the bullet is at app. 2700 fps and aim lower on what Deku's potential is.
With that said, 2700 feet per second translates to approximately 1780 miles per hour ( app. 4195 km per hour ). Since Deku is faster, I'll assume he's at 1800 mph to round things out, still underestimating his power.
Now, the speed of sound is about 767 mph, making him Supersonic ( about 2.35 times the speed of sound ). Now, later on he upgrades due to riled up emotions while fighting Bakugo, in which he tanks several explosions without major damage.
Anyways, the upgrade from 5-8% is about 160% ( 0.05 x 160% = 0.08 ). So, when I multiply 1800 by 160% (or about 1.6) I come up with a total of 2880 miles per hour, or approximately 3.75 times the speed of sound!
Then, you've seen that I upgraded him yet again in his fight against Duon up to 10%. This should be twice his 5% speed, putting him at 3600 mph, or about 4.69 times the speed of sound. In the manga, we see that he's reached the limit of twenty percent without major bone damage, though it feels as if his bones are on the verge of breaking. So, multiplying 3600 by 2, we get 7200 mph, or around nine times the speed sound. Boom.
But wait, there's more!
Five, eight, ten, and twenty percent is dandy and all, but what's his max? Well, to figure that out, I'll have to multiply our original five percent number ( 1800 ) by 2000%, or twenty. This comes from multiplying five by twenty to get one hundred. So, when that is all said and done, at the top of his game, Deku can move at 36000 MILES PER HOUR. That's FOURTY-SIX TIMES THE SPEED OF SOUND, making him Hypersonic at his max potential.
As my closing statement, all I can say is that I think our little chat earlier on Deku VS Ruby in terms of speed is officially settled. Eat it, Little Red Riding Hood.
Mic drop, suckas.