Email Subject Line Preview
Your subject and preheader as four inboxes will actually draw them.
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Tool input
Overview
About this tool
Renders a subject line and its preview text as a Gmail row on desktop and mobile, an Apple Mail row on an iPhone and an Outlook list row — each clamped to the width that client really gives it, with the cut shown in place.
Instructions
How to use it
Type the subject and the preheader — the first text in the email body, which every client draws beside or under the subject. Four inbox rows are drawn at the widths those clients actually use.
The preheader is half the preview
Leave it empty and the client fills the space itself, with whatever your first line of HTML happens to be — usually “View this email in your browser”. That is a quarter of your inbox real estate spent on nothing, and it is the most common unforced error in email.
Why the same subject fits in one client and not another
An inbox is a list of fixed-width rows. Gmail on the desktop pays for the sender column and the date first and gives the subject what is left, so it is the tightest surface here. Apple Mail on a phone is the most generous, with two lines of preheader under the subject. A character count cannot express any of that, which is why this measures width.
Questions
Frequently asked
How many characters should a subject line be?
That is the wrong unit. A subject is clamped by the width of the column it lands in, and the same character count fits or does not depending on which letters you used. Aim to land the promise inside the first thirty characters and check the widths here.
Are these widths exact?
They are each client’s default window at its default density. A maximised desktop window gives the subject more room; a split reading pane gives it less. Treat the last few pixels as a margin, not a line.
Do emoji help?
They earn attention and they cost width — an emoji is drawn at full width, so it is one of the widest characters you can spend. Some corporate filters strip them entirely, so never let one carry meaning your words do not repeat.
What about the from name?
It is drawn here because it competes for the same row, and on a phone it is read before the subject. A recognisable sender name does more for the open rate than any subject line trick.
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