What size ad can I run?

300×250 pixels. You can create an ad by selecting Build New Creative in the ad form, then filling out the form that appears. When uploading a book cover to the creative builder, use a cover image that is 115 pixels wide to ensure the best possible image quality. Alternatively, you can select Upload Existing Creative and submit a .png, .jpg, or .jpeg image. If you upload a very large image, the size will be reduced, which can negatively affect the quality of the image, so please aim to upload at the 300×250 size. Also note that you cannot use an animated .gif file.