Sprite size as a fraction of Viewport size

I want to find out the sprite size as a fraction of viewport size.

What I want to do is layout a set of tiles in a frame that is on the screen. The frame is another sprite, which is smaller than the whole game screen. To layout the tiles I am using:

childTransform.position = Camera.main.ViewportToWorldPoint(new Vector3(xNormalizedTilePosition, yNormalizedTilePosition, 1));

As you can see, it will be good to normalize the tile positions into a fraction of how big the frame is (i.e. the frame takes up 50% of the screen's x size, and 60% of the screen's y size).

Is there a way to do this?