Back to Tools

Email Subject Line Length Checker

Check how your email subject line displays across 12 major email clients. See exactly where truncation happens on Gmail, Outlook, iPhone, Yahoo Mail, and more.

About this tool

Your email subject line is the first thing subscribers see, and it gets truncated differently on every email client and device. Gmail mobile shows only 41 characters. Yahoo Mail mobile shows just 36 characters. If the most important part of your message gets cut off, your open rates suffer. This tool shows you exactly how your subject line appears across 12 major email clients so you can optimize it before sending.

Why subject line length matters

Research consistently shows that subject lines between 30 and 60 characters have the highest open rates. Shorter subject lines display fully on mobile devices where over 60% of emails are now opened. However, too short and you lack the context to compel a click. The sweet spot depends on your audience and content, but seeing the actual truncation points helps you make informed decisions.

Optimize for mobile first

With the majority of email opens happening on mobile, the first 35-40 characters of your subject line need to stand alone. Front-load the most important information and leave secondary details for the end. Pair your subject line with a strong preheader text that fills the preview space on clients that truncate your subject early.

Test before you send

Use this tool alongside the subject line tester which checks for spam triggers and emotional impact. Run your final subject through the spam word checker to avoid words that trigger filters. If you are A/B testing subject lines, our A/B test calculator helps you determine the right sample size for statistically significant results.

The preview text generator helps you craft the preheader that appears after your subject line in the inbox. Together, the subject line and preheader form the complete first impression your email makes.

Frequently Asked Questions

What is the ideal subject line length?

The ideal length depends on your audience, but 30-60 characters is the general sweet spot. This range ensures full visibility on most desktop clients while keeping enough context for mobile. For mobile-first audiences, aim for 30-40 characters. Campaign Monitor found that subject lines with 28-39 characters had the highest click-through rates.

Why does my subject line look different on every email client?

Each email client allocates a different amount of space for the subject line based on its layout, font size, and available screen width. Gmail desktop shows around 70 characters, but Gmail on a mobile phone shows only 41. Outlook desktop shows 73, but Outlook mobile shows 46. The differences come from the UI design choices each client makes.

Do emojis affect subject line length?

Emojis are technically 1-2 characters in length, but they take up more visual space than regular text. An emoji in your subject line will not drastically change the character count, but it may cause the text around it to shift slightly. Most email clients render emojis correctly, though Outlook on Windows may show them in black and white. Test with this tool to see the visual impact.

Should I optimize for desktop or mobile?

Optimize for mobile first. Over 60% of email opens happen on mobile devices, and this percentage continues to grow. This means writing subject lines where the most compelling part fits within 36-41 characters. Desktop users will see the full subject line anyway, so optimizing for mobile does not hurt desktop readers.

What is preheader text and how does it relate to subject line length?

Preheader text (also called preview text) is the text that appears after the subject line in the inbox. When your subject line is short, email clients use the preheader to fill the remaining preview space. A well-crafted preheader extends the story your subject line starts, giving you effectively two lines to convince someone to open your email.

Does subject line length affect deliverability?

Subject line length alone does not directly affect deliverability. However, extremely long subject lines (100+ characters) can look suspicious to spam filters. More importantly, subject lines that are ALL CAPS, use excessive punctuation (!!!), or contain known spam trigger words are more likely to affect deliverability regardless of length.

How do personalization tokens affect the length?

Personalization tokens like {{first_name}} or [NAME] are replaced with actual data when the email is sent. The token itself might be 14 characters, but the replacement could be 3-20 characters depending on the subscriber's name. Always test with both the shortest and longest possible replacement values to make sure your subject line fits across clients.

Are there any characters I should avoid in subject lines?

Avoid special characters that may not render consistently across email clients, including unusual Unicode characters, excessive punctuation marks, and some symbols. Standard letters, numbers, common punctuation (periods, commas, question marks), and popular emojis are safe. Dollar signs ($), percentage signs (%), and ampersands (&) work fine in most clients.

Compare email marketing software

Hands-on roundups to help you pick the right platform.

More Free Tools

View all tools

Subject Line Tester

Optimize your open rates with our AI-powered subject line tester. Get scores on emotional impact, length, and keyword effectiveness.

Email Preview Text Generator

Craft the perfect email preview text with real-time previews across 8 email clients. See exactly how your preview text will appear in Gmail, Outlook, Apple Mail, and more, with character limit warnings and ready-to-use HTML code.

Spam Trigger Word Checker

Scan your email content for words and phrases that trigger spam filters. Identify risky language that could send your emails to the spam folder and get suggestions for alternatives.

Email Hook Generator

Generate attention-grabbing opening lines for your emails across 8 hook categories and 4 tones. Browse 36+ proven hooks organized by type — curiosity, urgency, story, question, statistic, contrarian, personal, and problem — then copy the perfect opener for your next campaign.

Related reading