How much of your YouTube description actually shows

Search this and you will be told 125 characters. Or 100. Or 157. The numbers disagree with each other, they are never sourced, and there is a reason for that: YouTube does not publish one, and the thing being described is not measured in characters at all.

What YouTube actually documents

Two things. That a description is info that shows below your video, and that descriptions have a limit of 5,000 characters.

That page says nothing about the fold. Not how much shows, not where "Show more" falls, not that truncation happens at all. Every character count you have read for this question was written by somebody filling that silence.

So we measured it

On a real watch page, in Chrome, at two window widths. The collapsed description is three lines tall — 60 pixels — at both. What changes is the width of the column those three lines are drawn in: 1024 pixels in a full-width window, 844 pixels in a narrower one.

That is the whole answer, and it is why the folklore numbers fight each other. The cut is a line count, not a character count. How many characters fit into three lines depends on how wide the reader's window is, and on whether your text contains long words or links — a pasted URL eats an enormous amount of a line and can push your actual sentence out of view on its own.

Check yours in ten seconds

• —Open one of your own videos on a desktop browser.
• —Look at the description under the title, before you click anything. Read to where it stops and shows ...more.
• —Now narrow the browser window and watch the cut move. Same three lines, less text in them.

If your first visible line is your channel name, a greeting, or a stack of links, you have spent the only guaranteed real estate you have on something the viewer already knows or does not want yet.

What to do about it

• —Write the first sentence as its own job. It is the line that appears under your title in search and in suggested videos, and it is the one part of your description that survives every window width.
• —Keep links out of the top. A URL in line one can consume most of a line by itself. Links belong at the bottom, on their own lines.
• —Do not write to a character count. Write a short first sentence that is complete on its own, and the fold stops mattering.
• —Assume the rest is for people who already chose you. Everything past "Show more" is read by someone who has decided to watch. It is worth writing, and it is not doing the job the first line does.

What actually goes in those three lines, and in everything under them, is its own question: what to write in a YouTube description.

What this page does not claim

• —Not that YouTube documents any of the measurement. The 5,000 characters and "info that shows below your video" are theirs. The three lines are ours, taken on one day on one browser, and YouTube can change it without telling anybody.
• —Nothing about phones. We tried to measure the mobile layout and the reading did not survive its own check, so it is not here. An unverified number is how this question got into the state it is in.
• —Not that any of this changes your ranking. It changes what a human sees before deciding to click. That is a different claim and a smaller one.