Email Specs
Email Subject Line Length
Subject line length advice is usually given as a single number, which is useless because the visible length depends entirely on the client and the device. Here is what actually gets displayed, and how I write against it.
| Client and device | Visible characters | Note |
|---|---|---|
| Gmail, mobile app | About 35 to 45 | Varies with device width |
| Gmail, desktop web | About 70 | Preheader shares the row |
| Apple Mail, iPhone | About 35 to 40 | Two lines shown in some views |
| Outlook, desktop | About 60 | Depends on pane layout |
| Outlook, mobile | About 35 | Preheader shown below |
| Yahoo Mail, desktop | About 60 | Preheader appended |
| Item | Guidance |
|---|---|
| Visible preheader length | Around 35 to 90 characters by client |
| Practical target | First 40 characters carry the message |
| Fallback risk | Empty preheader pulls in body or alt text |
| Common fix | Hidden preheader div at the top of the body |
Notes
Front load the distinctive words. Because mobile clients cut around 35 to 45 characters, the decision is usually made on the first five or six words. Put the specific noun or number first and the brand context last, since the sender name already carries your brand.
Treat the subject and preheader as one unit of copy. The preheader should extend the subject, not repeat it and not read as boilerplate. An unset preheader is a real failure mode: many clients will pull whatever text comes first in the body, which is often an unsubscribe link or an image alt tag.
Length correlates with nothing on its own. In every test set I have run, specificity and relevance move open rates far more than character count. Use these numbers to make sure the good part is visible, not to hit a target.
Since Apple Mail Privacy Protection, open rate is a weak and inflated metric. Judge subject lines against click and conversion where you can, and treat open rate as directional only. Client display widths also change with app updates, so re-check in a rendering preview periodically.
Frequently asked questions
What is the ideal subject line length?
There is no single ideal. Aim for 30 to 50 characters so the whole line survives mobile truncation, and make sure the first 35 characters would work as a standalone subject.
Do emoji in subject lines help?
Sometimes, as a visual break in a crowded inbox, but they render inconsistently and can look off brand. Test rather than assume, and never use one as a load bearing part of the meaning.
Official sources
Platforms change specifications without notice. Check the primary documentation before a launch that depends on an exact value.
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