In depth
Everything you need to know about audiobook cover size
The short version of audiobook cover size: square. Make the cover 3000 × 3000 pixels in RGB, export a JPG of 72 dpi or more under 5 MB, and it meets the specs of ACX, Spotify for Authors, Voices by INaudio, Google Play and Kobo as their help pages read in October 2026. 2400 × 2400 is the most common minimum; 3000 gives you headroom.
The store-by-store audiobook cover dimensions are in the grid above, each linked to its source. Below: why audiobook covers are square, how to turn an ebook cover into one, and the file details that get covers sent back.
Why audiobook covers are square
Audiobook covers follow the shape of album art. Players and store pages show the cover as a square tile next to the playback controls, so a portrait ebook cover gets cropped or padded. Most stores now ask for a square file outright: ACX says the art must fill the entire 1:1 ratio and not be rectangular, and INaudio rules out borders and letterboxing.
Others will fix the shape for you, but not always well. Google Play letterboxes a non-square image into a square, and Kobo adjusts covers automatically. A cover designed square on purpose looks better than either.
From ebook cover to square: layout tips
Don't stretch or squash the ebook cover, and don't drop it onto a square background with bars at the sides. Rebuild it instead: extend the background art sideways, or crop a portrait illustration to its strongest square area, then reset the title and author for the wider shape. A title stacked on three lines on a 6 × 9 cover often reads better on one or two lines across a square.
Keep the look of the ebook so readers recognise the book, and check each store's content rules before adding anything new. ACX's audiobook cover art requirements say the title and author name must be clearly shown, and rule out pixelated text, Audible branding, references to running time or price, barcodes and QR codes, and photos of physical books or media.
File type, colour space and file size
Export in RGB, not CMYK. Print covers are often prepared in CMYK, and ACX lists RGB and 24-bit colour as requirements. JPG and PNG are accepted by every store above that takes uploads directly; TIF only by some (ACX and INaudio take it, while Google Play's delivery spec says TIF isn't supported and Spotify asks for PNG or JPEG).
Watch the file size. Kobo caps covers at 5 MB and ACX at 8 MB, so a high-quality JPG is the safe choice; very large PNGs can pass those limits at 3000 pixels. The dpi value is only a tag in the file, but ACX and Google Play's delivery spec ask for at least 72, so check that your export doesn't write a lower number.
Text legibility at thumbnail size
Most people first see your cover as a small tile in a store list or on a phone's now-playing screen. Before you export, shrink the design to about 150 pixels wide and look at it: if you can't read the title, make it bigger, bolder or shorter, and cut taglines and small print that turn into noise at that size.
Start from full-resolution artwork and real type, never an upscaled small image: ACX rejects pixelated or blurry text, and a cover that looks sharp as a tile can still look soft on a large screen.
Making the cover: what FullCastBook does and doesn't do
FullCastBook doesn't design or generate covers, so if you searched for an audiobook cover maker, this isn't one. Work with your designer or the ebook's source files, or use any image editor with a square canvas; the steps above are the whole job.
The audio is where FullCastBook fits. It narrates your manuscript with a distinct voice for every character, then exports one MP3, an M4B with chapter markers, or a ZIP with a file per chapter for stores that want one file per chapter. Where you can publish depends on each store's AI policy: as of October 2026, ACX requires human narration unless authorized, while Spotify for Authors accepts digital voice narration with a disclosure. See whether Audible accepts AI narration for the details.
Embedding the cover in your M4B
Stores take the cover as a separate image upload, so for publishing you don't need artwork inside the audio file. For your own library it's a nice touch: a tag editor that supports MP4 audio can add cover art to an M4B, and some library apps, Audiobookshelf among them, let you set a cover for each book.
FullCastBook's M4B export carries the title, author and chapter markers but no embedded image, so add the cover afterwards if you want it on your phone. More answers about formats and exports are in the FAQ on the home page.
