Size ratio according to iPhone size :
Here's what you can do to have different width and height for cell's regarding the iPhone size :
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
let width = (self.view.frame.size.width - 12 * 3) / 3 //some width
let height = width * 1.5 //ratio
return CGSize(width: width, height: height)
}
And maybe you should also disable your AutoLayout constraints on cell for this answer to work.