Why pixels, not just characters
Google doesn't cut titles off at a character count. It cuts them off when they run out of horizontal space, so the real limit depends on which letters you use. WWWWWWWWWW and iiiiiiiiii are both ten characters, but the first is several times wider than the second. A 55-character title full of capitals and wide letters can be truncated while a 65-character title in lower case fits.
That's why this tool shows two measurements. The character count is graded against the same bands the main Meta Tag Checker uses (30–60 for titles, 120–160 for descriptions), because characters can be counted reliably on any page. The pixel width is what actually decides truncation, and it drives the preview.
How the measurement works
Your browser renders the text in Arial at the sizes Google uses on desktop results (20px for titles, 14px for descriptions) and measures how wide it comes out. The title is then compared with a limit of about 580 pixels and the description with about 920 pixels. Text past the limit is cut at the last whole word and given an ellipsis, as Google does.
Treat those limits as good approximations, not guarantees. Google doesn't publish them, results pages change, mobile results use different widths, and devices without Arial substitute a font with near-identical widths. Google also sometimes rewrites titles and descriptions entirely, for example when it thinks another part of the page answers the search better. A title that fits here is one Google can show in full, not one it promises to.
What to aim for
- Titles: keep the words people search for near the start, where they survive truncation. Aim to fit within the pixel limit. If you can't, make sure whatever gets cut off is expendable, like your brand name. More in title tag best practices.
- Descriptions: put the reason to click in the first 120 characters, because mobile results show less than desktop. See how to write a meta description.
To check the rest of a page's tags as well (Open Graph, Twitter cards, canonical, headings and image alt text), run the full Meta Tag Checker.