There is no single real confirmed measurement but we might be able to make one ourselves using pixel measurements.

There's actually an official sprite we can use for this, the soccer ball


If you get the measurements from a real soccer ball you'll find it's roughly 22 centimeters in diameter, and because the scratch ball is 47 x 46 pixels (We can assume the missing pixel from the top is just because the ball is missing air) we end up with this

22cm - 47px
x - y

We can then do

22cm - 47px
x - 1px

Which is exactly 0.46808510638 or roughly 0.47cm
This means the scratch stage measures 224.68 centimiters in width, that's around 2 and 1/4 meters or 7.38 feet of width which is enough to fit a regular person and if you think about it is even kind of to-scale with the scratch cat! as the average cat is 50~ centimiters in lenght!

This has been my game theory, only did this because I wanted to know how big stuff was in my physics engine project

https://scratch.mit.edu/projects/1330190717/

That's interesting! I never thought about that! What measurements do you get if you base it off other sprites? They have sprites for people!

Edit: I get 168 cm in height! that is about the size of a child. therefore, some of their sprites are heavily undersized! (A ball is not half the height of a small person)

Interesting