The two different character limits every ad platform has
One number gets your ad rejected. The other lets it run with the sentence cut in half. Most guides publish only one of them.
Every ad field has two limits, and conflating them is why copy that "fit" still reads as a fragment in the feed.
- The hard cap. Past this, the upload is refused.
- The visible limit. Past this it runs, and gets truncated behind a "see more" or an ellipsis.
They can sit a long way apart
LinkedIn's single image ad takes a headline of up to 200 characters and cuts it at 70. Its introductory text takes 3,000 and cuts at 150. YouTube's in-feed headline takes 100 but anything past 25 "may be shortened on some devices".
So a 120-character headline is a truncation on LinkedIn and a flat rejection on X, where the cap is 70. Same copy, different failure.
The link tax on X
X states that each link used reduces the character count by 23, "electing 257 characters for X copy". Every ad has a destination, so 257 is your real budget and anything written to 280 won't fit.
Write to the visible number
A headline that fits the cap but gets cut off mid-word is a worse ad than a shorter one. Write to the visible limit and treat the cap as headroom.