How To Write Email Subject Lines Calculator
A subject line has one job and about forty characters to do it in. Everything else in the email is invisible until that job is done.
Every line is a formula rather than a finished sentence, so it can be edited without losing the reason it works. The character count and the mobile verdict are the parts worth checking before you send.
Get it opened — subject lines
Autumn sale starts today for subscribers
40 chars6 wordsfits mobile
Your autumn sale picks are ready for subscribers
48 chars8 wordsmay truncate
Is autumn sale worth it?
24 chars5 wordsfits mobile
The autumn sale questions you asked for subscribers
51 chars8 wordsmay truncate
What we learned about autumn sale
33 chars6 wordsfits mobile
Before you spend on autumn sale
31 chars6 wordsfits mobile
- Lines generated
- 6
- Shortest
- 24 chars
- Median
- 36.5 chars
- Average
- 37.8 chars
- Longest
- 51 chars
- Fit a phone screen
- 4 of 6
- Spam triggers
- 0
Mail clients cut a subject at roughly 41 characters on a phone and about 60 on a tablet, so anything longer is only half read. Words that trip spam filters are flagged even when the line reads naturally.
The formula this calculator uses
subject = one concrete noun + one reason to open, kept under 41 characters
- L
- Length of the subject line in characters
- T
- The truncation threshold for the mail client
How to check the result by hand
- 1
Write the topic down as a noun, not a benefit
Name the thing: the product, the season, the event. Benefits are what the body is for, and a subject built on a benefit usually reads like every other subject in the inbox.
- 2
Choose the action you want
Opening, clicking and replying need different lines. Picking the action first stops you writing six variations of the wrong thing.
- 3
Generate and count
Each line comes with its character count. The count is the whole point, because it decides whether the second half of the line is ever seen at all.
- 4
Check the phone verdict
Anything past forty one characters will be cut on a phone. Read only the prefix that survives and ask whether it still says what the email is about.
- 5
Clear the spam words
A flagged word does not doom the email, but it moves it towards the junk folder. Rewording is usually cheaper than living with the flag.
For worked examples, common mistakes and the limits of this formula, read the full How To Write Email Subject Lines page.