How long should a subject line be (character limits across clients)?
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Your subject line gets cut off differently depending on where your subscriber is reading. Mobile screens are the tightest: most show 30-40 characters before truncation. Gmail on desktop gives you 60-70. Outlook desktop varies based on the reading pane width. Apple Mail on desktop tends to be the most generous.
The practical implication is simple: write for mobile first. If the first 35-40 characters of your subject line don't tell the story, a significant portion of your audience will never see the rest. Front-load the most important words. "25% off everything this weekend" works better than "This weekend only, everything in the store is 25% off" because the meaningful part lands before the cut.
But That said, there's no universally correct length. A 55-character subject that communicates your message clearly is better than a 30-character one that's vague. The goal isn't minimum characters. It's making sure nothing essential gets chopped. If you want to see exactly how your subject will appear, previewing across clients before sending is the only way to know for sure. Preheader text can also carry overflow context that the subject can't fit. Preheader text is worth treating as a second subject line slot, not an afterthought.
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