By placement

Vertical feeds — Reels, TikTok, Shorts: 15 to 30 seconds. The first two seconds decide whether the rest is watched at all, so the hook goes at frame one and the title comes second.

Your own site, a newsletter, a retail page: 45 to 60 seconds. The viewer arrived on purpose, so a little more patience is available — enough for a voice, a world and a question.

Anything longer is a different object: an author film, a launch piece, a festival cut. Those have their uses, but they are not trailers and should not be measured as trailers.

What each length can hold

Fifteen seconds holds one idea. One image, one line, one title card. Attempting two ideas in fifteen seconds delivers neither.

Thirty seconds holds a turn — a world established, then something that threatens it. This is the most useful length in existence for a novel.

Sixty seconds holds a voice. It is long enough for actual narration to breathe, which is why it is the right length when the trailer is advertising an audio or film edition rather than the book alone.

The rule underneath all of it

Cut for the shortest length that still lands, then stop. Length is not effort and duration is not value; a tight thirty outperforms a loose ninety on every platform that has ever been measured.

Build the long cut first if it helps you think, but deliver the short one. The Proclamation runs to 180 seconds for business advertisements because a business often has a case to make. A novel rarely does — a novel has a spell to cast.

Asked and answered

Does a longer trailer cost more here?

For an advertisement, yes — the Proclamation adds $100 per additional 30 seconds in either vessel. A film book is priced on word count, not on trailer length.

Should the trailer show my cover?

Yes, and at the end. Leading with the cover spends the hook on an image the viewer cannot yet care about.

Do I need different cuts for different platforms?

At minimum a vertical short cut and a horizontal longer cut. Same footage, different rhythm and framing.