# Audiobook file specs: retail sample, loudness, and cover size > The numbers stores actually check: sample under 300 seconds, 2400 square cover, −23 to −18 dB loudness, and 2-second silence pads. Canonical: https://lex.audio/how-to/publish ## Introduction Publishing is proof, package, and approve. You're locking the final audiobook before it hits a store upload. Stores don't care about your story. They reject technical misses. This chapter covers listening against the manuscript, fixing flagged lines, assembling chapters, cover and metadata, file specs, and sign-off. If you're still recording, go back to [How to narrate](https://lex.audio/how-to/narrate). - **Proof:** catch wrong words, skips, and bad takes - **Package:** chapters, credits, sample, cover, metadata - **Approve:** your OK means upload can start ## Proof the narration against the manuscript Listen while you read the manuscript. That's the whole job. You're checking that what's on the page is what's in the audio. Watch for dropped words, wrong names, skipped lines, repeated lines, and flat or rushed reads. Flag anything that would make a listener stop. A synced transcript helps: spot mismatches without scrubbing blind. Timestamp every flag. Proof the full book if you can. At minimum, hit every chapter opening, every character name change, and any glossary or made-up terms. ## Fix flagged lines One note per issue. Include a timestamp or line number and what's wrong. "Chapter 4, 12:08, says 'Marcus' should be 'Markus'." That's enough. Request a retake on that line when you can, not a full chapter redo. Full chapter retakes cost time and can introduce new errors. 1. Listen and flag 2. Write one clear note per flag 3. Get the line fixed 4. Re-listen only the fix plus a few seconds around it When the flagged list is empty, you're done with proof. Move on to assembly. ## Assemble chapters into a finished audiobook Chapters go in book order. Opening credits first. Closing credits last. Nothing else in between those bookends unless your store requires it. **Opening credits** need title, author, and narrator. **Closing credits** need an ending cue (narrator, production credit, or similar). Each chapter file should start and end clean. Stores want 1 to 5 seconds of head and tail silence. Target about 2 seconds on each end. - Chapter titles spoken at the top, or clear markers per store rules - No music bleeding into silence pads - No clipped endings - Consistent volume chapter to chapter Export one MP3 per chapter from your DAW or mastering tool, named in order so upload stays boring. ## Package cover art and metadata Cover art is a square 2400×2400 JPG. No letterbox borders, no thin frames, no text hugging the edge. Stores rejected bordered covers in August 2026. Fill the square. Lock metadata before upload: - Title and subtitle (if any) - Author and narrator - Series name and book number (if applicable) - Description - Genres or categories - AI or synthetic voice disclosure fields where the store asks Match spelling to the manuscript and the audio. A mismatch between cover, metadata, and credits is an easy bounce. ## Choose file formats and delivery Stores want chapterized MP3s at 44.1 kHz and a store-safe bitrate. Master to retailer loudness before you upload. You also need: - **Opening credits** as its own track, under 3 minutes - **Closing credits** as its own track, under 3 minutes - **Retail sample** (`sample.mp3`) strictly under 300.0 seconds. Aim for about 4:30 to 4:54. Samples over 5:00 get bounced. Loudness should sit around −23 to −18 dB mean. Keep peaks store-safe (about ≤ −3 dB for ACX-style DIY; some wide portals gate hotter peaks closer to −1 dB). Quiet credits and hot chapters are common bounce reasons. ## Get final approval Do one last listen before you approve. Hit the retail sample and the first chapter at minimum. You're not re-proofing the whole book. You're confirming nothing broke during assembly. - Sample plays clean and stays under 300.0 seconds - First chapter opens with the right title and narrator credit - No clicks, clipped words, or dead air at the top - Cover and metadata match what you hear When you approve, upload can start. Treat approval as final. Stores don't love replaced files after go-live. ## Move to distribution Once the package is approved, you're ready to list. Distribution is the next step: pick stores, write the listing, set price, and launch. Read [How to sell](https://lex.audio/how-to/sell) for store choice, pricing, and launch. For a store-by-store breakdown of wide vs DIY paths, see [Distribution](https://lex.audio/distribution). ## Common questions ### How long can an audiobook retail sample be? Strictly under 300.0 seconds. Aim for about 4:30 to 4:54. Samples over 5:00 get bounced. ### What size should audiobook cover art be? A square 2400 × 2400 JPG. No letterbox borders, no thin frames, and no text hugging the edge. Stores began rejecting bordered covers in August 2026. ### What loudness should an audiobook be mastered to? Around −23 to −18 dB mean. Keep peaks store-safe: about ≤ −3 dB for ACX-style DIY, while some wide portals gate hotter peaks closer to −1 dB. ### How much silence goes at the start and end of a chapter? Stores want 1 to 5 seconds of head and tail silence. Target about 2 seconds on each end, with no music bleeding into the pad and no clipped endings. ### What audio format do audiobook stores require? Chapterized MP3 at 44.1 kHz at a store-safe bitrate, one file per chapter, plus opening and closing credits as their own tracks under 3 minutes each.