Let’s use his feat at Enies Lobby for example. He successfully shot down several Marines across an incredibly long distance through a very windy day. But how far WAS it?
Here’s a picture of Dorry about to fight Luffy
Luffy is 5′7 according to the One Piece wiki. Stacking him up against Dorry makes the giant 13 Luffys tall.
Run that through the calculator 13 times and you get 72 feet and 7 inches.
Now let’s assume that’s the average height of a giant. Hang in there, we still have a bit to go
Here is two giants bending down in front of the main gate. When you bend down like that, you drop about 2 feet (I measured myself with a tape measure for this). Bent down, they’re about as tall as the main gate. So let’s assume the main gate is 70 feet tall.Here is the main gate compared to the Tower of Justice.
Not counting the flagpole it’s 3 Gates tall. Which makes the Tower of Justice 210 feet tall.
Now here is the MASSIVE Gates of Justice
Stacking the tower on top of each other (Not counting the flagpole again) we see how tall it is. We can’t see the top of the curve in this picture, so we can only assume it’s 6 towers tall. Run that through the calculator and the gates are 1260 feet tall
Now here we CAN see the whole door (I didn’t use this picture since the tower here is bigger, and this is more of a perspective shot).
Taking the tower from our previous picture and going from the sides to the middle, each gate is 810 feet long.
Trust me, you’ll see where I’m going with this
Here’s the Bridge of Hesitation, where several Marines were shot down by Usopp.
With the open gate in the background, putting them up against each other makes the bridge 2 and a half gates long 840 x 2 + 420 (*snicker*) The Bridge of Hesitation is 2100 feet long
But wait! What about the water in-between the tower and bridge? While this is an angled picture, this is as good as I can get.
The distance between the bridge and tower is about 3 bridges long with the third bridge going behind the tower due to the perspective. Which makes it 6300 feet long.
So after all of these calculations….we can come to this conclusion.
Usopp was able to successfully snipe off several Marines and save Robin while standing at a height of 210 feet at targets that were 6300 feet away, with severe wind, while using A FREAKING SLINGSHOT.