Aim for a subject line that stays readable everywhere. Mobile inboxes cut off around 33 characters, most desktop clients around 60.
Free Email Subject Line Length Checker
Check your email subject line's length against mobile, Gmail and Outlook cut-off points so it never gets truncated in the inbox — free, instant and private.
What is the email subject line length checker?
An email subject line length checker is a free tool that shows whether your subject line will display in full or get cut off across email clients. You type your subject line and it counts the characters live and tells you if it fits on mobile (which truncates around 33 characters), Outlook (around 60) and Gmail on desktop (around 70). Slashit's checker runs in your browser, so nothing is uploaded, and it helps marketers and anyone sending email write subject lines that land the key words before the cut-off — where they actually get read.
How our free email subject line length checker works
Type your subject line
Enter the subject line you're planning to send.
See the live count
The character count and a progress bar update as you type.
Check each inbox
Chips show whether it fits or gets cut off on mobile, Outlook and Gmail desktop.
What can you use the email subject line length checker for?
Checking a subject line before a campaign send
Once a newsletter goes out you can't fix a truncated subject line. Checking the length first is a two-second insurance policy.
Writing for mobile inboxes
Most email is opened on a phone, where far fewer characters are visible than on desktop. Front-loading the message matters more than total length.
A/B testing variants
Comparing several subject lines side by side helps you pick between them on length and clarity, not just gut feel.
Auditing an automated sequence
Onboarding and drip sequences are written once and run for years. Reviewing every subject line catches ones that get cut off.
Who uses our free email subject line length checker?
Email marketers
Make sure the important words land before the mobile cut-off.
Newsletter writers
Write subject lines that display in full across clients.
Sales & outreach teams
Keep cold-email subject lines short and readable on phones.
Why use the email subject line length checker?
Multi-client preview
See mobile, Outlook and Gmail cut-offs at a glance.
Live feedback
The count and status update instantly as you edit.
Free & private
No sign-up, and your subject lines stay in your browser.
How much of your subject line is actually visible
Display limits vary by client and device — these are practical guides rather than hard rules.
| Where | Roughly visible |
|---|---|
| Gmail on desktop | About 70 characters |
| Gmail on mobile | About 35–40 characters |
| Apple Mail on iPhone | About 35–40 characters |
| Outlook desktop | About 60 characters |
| Practical target | Under 50 characters |
Tips for getting the best results
Put the important words first
Assume the end will be cut off on mobile. If your subject still makes sense from the first 35 characters, it works everywhere.
Avoid all caps and exclamation marks
They read as shouting and are a well-known spam signal. A specific, plain subject line outperforms an urgent-sounding one.
Use the preview text deliberately
The preheader is a second line of copy most senders waste. Write it to extend the subject rather than repeating it.
Be specific rather than clever
“Your March invoice is ready” beats “A little something for you”. Clarity gets opened; vagueness gets ignored.
Frequently asked questions
What's the ideal subject line length?
Around 30–40 characters is safest so it isn't cut off on mobile, where most email is now opened. Under ~60 keeps it readable on most desktop clients too.
Why do subject lines get cut off?
Each email app shows only so many characters before truncating with an ellipsis. Mobile shows the least, so front-load your key words.
Is it free?
Yes — it's free, needs no sign-up, and runs entirely in your browser.
How long should an email subject line be?
Under about 50 characters is the practical target. That survives truncation on mobile, where most email is now opened.
Does subject line length affect open rates?
Length itself matters less than whether the point survives truncation. A subject cut off mid-sentence on a phone loses its meaning, and that's what costs opens.
What makes a subject line look like spam?
All capitals, rows of exclamation marks, “FREE” in caps, excessive emoji and exaggerated urgency are all common triggers. Plain, specific language performs better and is less likely to be filtered.
Should I use emoji in subject lines?
One well-chosen emoji can help a message stand out, but it renders differently across clients and some corporate filters dislike them. Never rely on an emoji to carry meaning.
