What's the size of brochure?

Letter A4. 81/2 x 11 - Open for discussion.

Sorry to be so obscure. I''d like to leave it open for creative element. I am good either way with single page, front and back that would be a larger version of a business card with content.
 
I am also open to A2 folded 4 page with content on the front back and in the middle like a presentation folder which would also leave room for our own brochures and business cards.