Email Subject Line Length Checker

The Email Subject Line Length Checker measures each subject line you paste and tells you whether it will display in full or get cut off in a typical inbox. It reports the character count, an estimated pixel width, and separate verdicts for mobile and desktop, so you can see at a glance which subjects are the right length and which are likely to be truncated before the reader finishes them.

It is built for email marketers, newsletter writers, and anyone who cares about open rates, because the subject line is the first and sometimes only thing a recipient sees. Inboxes cut subjects off at different points on phones and computers, and a great subject that ends in an ellipsis loses its impact. Checking length before you send helps you front-load the important words and stay within the visible window.

Everything runs locally in your browser using JavaScript, with no uploads and no account. Paste one subject line or a whole batch, one per line, and click Check to get a table of results plus summary statistics. Because the analysis happens on your device, your subject lines and campaign ideas remain private and are never sent to or stored on any external server.

Features

• Counts the exact number of characters in each subject line so you know precisely how long it is.
• Estimates the rendered pixel width, since many inboxes truncate by available space rather than character count.
• Gives separate Fits or Truncated verdicts for mobile and desktop based on typical inbox display widths.
• Assigns an overall verdict of too short, ideal, good, or too long to guide quick editing decisions.
• Checks many subject lines at once, one per line, and returns a row for each in a sortable results table.
• Summarises how many subjects fall in the ideal or good range so you can review a whole batch fast.
• Exports the results table to CSV or XLSX, or copies it to your clipboard for sharing with your team.

How to use Email Subject Line Length Checker

1. Paste one subject line, or a batch with one subject per line, into the input box to analyse them together.
2. Click the Check button to measure each line's character count and estimated pixel width instantly.
3. Read the mobile and desktop columns to see whether each subject fits or will be truncated on each device.
4. Use the overall verdict column to spot subjects that are too short, ideal, good, or too long at a glance.
5. Check the summary stats to see how many of your subjects land in the recommended length range.
6. Copy or export the table, then revise any subjects that are too long so the key words appear early.

Benefits

• Protects open rates by ensuring the most important words appear before the inbox truncates the subject.
• Highlights subjects that are too long for phones, where a large share of email is now first opened.
• Speeds up A/B preparation by letting you length-check several candidate subjects in a single pass.
• Removes guesswork about what fits, replacing it with clear character, pixel, and device-based verdicts.
• Keeps campaign ideas private because all measurement happens locally in your browser on your device.
• Helps teams standardise on subject-line guidelines with an exportable, shareable table of results.

Inbox providers do not truncate subjects at a single fixed character count; they cut them off based on the width available in the reading pane or list view, which varies by device, screen size, and font. That is why this tool reports an estimated pixel width alongside the raw character count, using a typical average character width to approximate how much space a subject occupies. Treat the pixel figure as a helpful estimate rather than a pixel-perfect measurement.

As a practical rule, subjects around forty to fifty characters tend to display in full across most devices, while very short subjects can feel abrupt and very long ones risk being cut off on mobile. The tool flags subjects below roughly twenty characters as potentially too short and those above sixty as likely too long, but your own audience and template matter, so use the verdicts as guidance rather than strict limits.

Because all analysis runs in your browser with JavaScript, your subject lines are never uploaded or stored, keeping unreleased campaign ideas confidential. Remember that emoji and wide characters can occupy more visual space than their character count suggests, and that preview text shown after the subject also influences the open decision. Use the length check together with strong, front-loaded wording for the best results.