1. A method for providing one or more content items for a content item slot, comprising: receiving, by one or more data processors, a height and a width of a content item slot of a resource, wherein a ratio of the height of the content item slot to the width of the content item slot is a non-standard content item slot ratio, and wherein no format parameter associated with a pre-defined slot size or slot ratio is received; receiving, by one or more data processors, one or more requesting device parameters, wherein the one or more requesting device parameters comprise at least one of a browser type, a browser version, and an operating system; determining, by one or more data processors, a number of content items based on the height, the width, and a minimum content item size, wherein the minimum content item size is based, at least in part, on the one or more requesting device parameters; selecting, by one or more data processors, one or more content items equal to the determined number; formatting, by one or more data processors, the one or more selected content items based, at least in part, on the minimum content item size, the height, and the width; and outputting, by one or more data processors, data to effect display of the one or more formatted content items.