Alright. So you want to play the calc game, let's play the calc game.
Pica's clenched fist is already half as wide as Pica's upper body.
And that's just his clenched fist as I pointed out. His open palm, that would basically double the size.
Let's take other examples:
Pica's palm is just overproportionally big.
And Hajrudin is at least as big as a six story building.
So let's make a "calc". Hajrudin = 2x3 store building (taken from Pica's finger):
So the clenched part of Pica's hand makes up the length of 6x Hajrudin. Makes it 6x22m = 132m. And we learned that Pica's overproportional fist is = 2x his upper body. 2x132 = 264m. So Pica's upper body is 264m tall. And as we witnessed, Pica's upper body makes up more than 2/3 of his height; his legs are tiny:
264m (upper body) * 1.5 (as the lower body is half the size) = ~396m. And since the legs are even a bit less than 1/3 of Pica's overall height as you witnessed from this picture, my prediction of 360m might actually be true.
No matter how you try to argue around it, it won't change that fact.
But then again, Oda himself doesn't care about the exact scale and is very inaccurate. The best way to measure it, is to compare Pica to the 48m tall Colosseum. Seeing Hajrudin fighting in the arena with his 22m, you can see that is is not far off from being half the height of the Colosseum walls. You might be generous and say 3x Hajrudin = Colosseum walls. Heck. Say it takes 4 Hajrudins. That's 80m*4 = 360, as the Colosseum was displayed as 1/4 of Pica's height.