It measures 500 across the smaller points 900 across larger points and 750 from centre to the largest single points.
I found the centre of a 900 sheet of coro and drew the 2 circles. 500 and 900. A nail in the middle with a piece of string works great for circles, then I just divided it up.
A few people have asked for dimensions of my star so I created a quick drawing on how to draw my star on a 1200x900 piece of coro. The inside circle is radius but this can be modified to suit how pointy you want the star. Same process applies. Good Luck