Your title tag is the largest, most clickable line in a search result, and it is a genuine ranking signal. The title tag length checker measures your title by character count and by estimated rendered pixel width, and previews it as a search result so you can see whether Google is likely to cut it short.
Pixels, not characters
Search engines decide where to truncate a title based on its rendered width in pixels, not its character count. Because letter widths vary widely, a title full of wide letters can be clipped while a longer title of narrow letters fits. This tool measures pixel width in the font size Google uses for titles, so its warnings track real truncation far better than a simple character limit. A practical desktop target is around 580 pixels, or roughly 50 to 60 characters.
Put keywords first
Whatever survives truncation should carry the message. Lead with your primary keyword and the page’s core promise, and push the brand name or secondary terms toward the end where a cut does least damage.
Google may rewrite it
Google sometimes replaces a title with your H1 or another on-page phrase when it judges that a better fit for the query. A well-sized, descriptive, unique title improves the odds your version is the one shown — and a distinct title per page avoids the “duplicate title” pitfalls that trigger rewrites.