Whilst there are no hard and fast rules as to how big the squares are there are a couple of videos on YouTube that show this block.
The first is from the Quilt Codex channel and uses yardage to rotary cut and sew the squares individually. The final block using the sizes given is eight and a half inches unfinished.
The second is by the wonderful Jenny Doan from the Missouri Star Quilt company and uses layer cake (10 inch) squares to make what she is calling "the Ground Cover Quilt".
And finally here is what you get with the same block when two of the smaller squares are the same colour as the background and the whole thing is set on point