Game area

Hello everyone!
I am using phaser 3 and matter physics engine.
I am creating circular images on pointer down.
I need to know how much is the area of a circle I create and the area of the game area. By this I will be able to know how many percent of the game area is covered by the circles created.
Currently I have this: https://glitch.com/~game-playground
I can calculate a circle’s area, I guess. But do not know the area of the game area.
How can I achieve this?

Phaser.Geom.Rectangle.Area(this.cameras.main)

should do it.

I had used this.cameras.main.width*this.cameras.main.height and I guess it is the same thing. Right?
If so it is a confusion point. I cannot find these things in the docs like never. Redundancy adds up to the complexity of the documentation of this project. Just a feedback.