How do I Know How Big To Make My Sprites?

I know that when a Sprite Sheet is imported, Construct 2 chops it into identical squares. How big are the squares?

I have a sprite, H: 320px W: 102px. The strip I am trying to import is H: 2560px W: 102px.

However, when I import it, Construct 2 only imports a fraction of the strip. I take this to mean that my sprites are too big?

Do I have to make my sprite smaller, or is there a better way of importing it?

Are you importing it into a TiledBackground?

Or. As a Sprite Strip into a sprite ?

https://www.scirra.com/manual/53/import-sprite-strip

I'm importing it as a sprite strip into a sprite; 1 vertical cell, 8 horizontal.

I just realized that I was switching the horizontal and vertical cell count... it should have been 8 vertical, 1 horizontal. Thanks for that link!