Hi,

I'm making this cake - https://sugargeekshow.com/news/how-to-make-a-cake/ , which is 3 6 inch by 2 inch cake layers filled. How tall will my cake be? I am planning on using the 12 inch wide by 6 inch tall wilton cake box - https://www.amazon.com/Wilton-12-Inch-Window-10-Inch-2-Piece/dp/B00C2O4PS0/ref=sr_1_6?keywords=wilton+cake+box&qid=1571154550&sr=8-6 and an 8 inch cake circle. 

Will it fit in a 6 inch box....the cake looks pretty tall :).... thank you!

No it will not fit in a 6" tall box.  The cake layers alone, if 2" tall each, will be 6".  Torted and filled, they will probably be at least 7" and with the frosting on top, closer to 9".    To me, that is how the cake appears in the picture, about 6" x 9" to the top of the frosting peaks.

Also, for a 6" cake, I always use at least a 10" base or larger.

Wilton makes

Wilton makes an adjustable box that will fit up to 9in I think.  I've had to tape dowel inside the box before to the top didn't go too far down. Now I just used plain 14x14 cardboard boxes I order in bulk

I do what Caketally noted, tape straws into the corners of the box to add height for the lid.