See where every inbox cuts your subject line off
Type a subject and preheader — or paste your email HTML and we will pull them out — and watch ten real inbox rows truncate them. Measured in pixels, because clients clip where text runs out of room, not at a character count.
Free · no signup · measured, not estimated
Why character counts are the wrong unit
Every free subject-line tool counts characters. No email client does.
An inbox list is a narrow column with text-overflow: ellipsis on it. The client lays your subject out in its own font and cuts it at the pixel where the column ends — so the same “41 character limit” lands somewhere different for every subject you write. Capitals are wide, lowercase is narrow, an i takes a third of the room of a W.
So this tool measures instead of counting. It asks the browser for the real advance width of your glyphs in that client’s font stack, wraps word by word, and clips the final line at the exact pixel. The output is not a number — it is the text that survives.
What the rows tell you
Three findings that only appear when you look at the list view rather than the email.
- 1
Where each client cuts
Sender, subject and snippet are measured separately, and each row says which of the three got cut. Single-line clients share one row, so a long subject squeezes the snippet out of it entirely.
- 2
Where your snippet comes from
With no hidden preheader container, the client scrapes the first body text it finds — usually "View in browser" or a nav link — and shows it beside your subject to everyone. The finding most people do not know they have.
- 3
What is wrong with the copy
Shouted capitals, punctuation pile-ups, a fake "Re:" prefix, unrendered merge tags like {{first_name}}, value buried at the end of the sentence, composed emoji that can split, and a preheader that repeats the subject.
The preheader nobody authored
A preheader is not a field in most ESPs — it is a hidden div at the top of your HTML that clients scrape for the snippet. Leave it out and nothing goes blank: the client takes whatever text it finds first, which is why so many campaigns go out with “View this email in your browser” beside their subject. A short preheader does not stop it either — the client appends the body text that follows.
- Says whether your snippet is authored or scraped, and shows the text either way
- Detects a preheader that just repeats the subject, wasting the second line
- Detects the zero-width padding technique (U+200C plus non-breaking spaces) — both when it is used and when it is missing
Write the front half like it is the whole thing
Truncation is a pixel boundary you do not control, so the reliable technique is front-loading: put the thing that makes someone open the email in the first few words. “Free shipping ends tonight” survives every row here; “We wanted to let you know that free shipping ends tonight” arrives on a phone as “We wanted to let you know that…”.
- Front-loading is flagged when the value sits late in the sentence
- Sender name is measured too — it takes a third of the row on single-line clients
- Every field is editable in place, so you can rewrite and re-measure without leaving the page
More free email tools
Every one of these runs in your browser, needs no account, and has no usage limit.
Subject lines and preheaders, answered
- How long should a subject line be?
- Length in characters is the wrong question, and it is why every "keep it under 41 characters" rule contradicts the next one. Clients truncate when the text runs out of pixels, so a narrow subject like "Illinois vs. Wyoming" (21 characters) takes far less room than "MASSIVE SUMMER SAVINGS" (22 characters). Write the subject you want, then look at the rows above and check that the part that carries the meaning survives in the narrowest client your list actually uses.
- How many characters does Gmail show in a subject line?
- The figures that circulate — Gmail on Android around 33 characters, Gmail on iPhone 37, Apple Mail on iPhone 48, Outlook on the web 51, Gmail on the web 88 — are averages of average-width English text, usually measured once, on one device, at one zoom level. They are a useful calibration target and a terrible rule. We use them as exactly that: each of the ten client specs in this tool records which published figure its column width was fitted against, and what that implies about window size, so you can check our work.
- Why does this tool not show a character count?
- Because a character count would be a made-up number dressed as a measurement. We measure real glyph advances with the canvas text API, at each client’s own font stack, font size, font weight and column width, then wrap word by word and clip the last line exactly as the browser does. The tool returns the visible text instead of a count.
- What is a preheader, and why does mine say something strange?
- The preheader is the snippet a client shows next to your subject. If your email has no hidden preheader container, the client scrapes the first text it finds in the body — which is usually "View in browser", a nav link, or an unsubscribe line, and that goes out beside your subject to your whole list. The tool tells you which of the two happened: an authored hidden preheader, or a body-text fallback.
- Which inbox clients are measured?
- Ten rows: Gmail on the web (including the Promotions tab variant), Gmail on Android and iPhone, Apple Mail on macOS and iPhone, Outlook on the web and Windows, Yahoo Mail, and Samsung Mail. Each spec records the published character figure its column width was fitted against, so the calibration is auditable rather than asserted.
- How accurate is the truncation?
- It is a real measurement of a modelled inbox, not a screenshot of yours. Two honest caveats. Inbox widths are elastic — a maximised 27-inch Gmail window shows much more than a split-pane Outlook, and each spec models a common default rather than your reader’s actual window. And the canvas resolves the first available font in each client’s stack, so a machine without Google Sans or Segoe UI falls further down the stack and shifts the numbers slightly. The ranking between clients, and the point where your own subject gets cut, hold either way.
- Do emoji in subject lines help?
- They earn attention in a crowded list, and they carry two risks worth knowing. A composed emoji — a family, a skin-tone modifier, a flag — can split into its component glyphs in an inbox list that lacks the font, and a screen reader reads the emoji’s full CLDR name out loud in the middle of your sentence. The tool flags composed sequences specifically rather than telling you to avoid emoji.
- Does the preheader affect deliverability?
- Not directly. It affects open rates, because it is half the copy a reader sees before deciding. The one deliverability-adjacent case is the padding trick — a long run of zero-width non-joiners and non-breaking spaces used to stop the client scraping body text. It works, and if it is the only content of your preheader, the snippet is simply blank. The tool detects both.
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