Work
The truncation threshold
The client shows only the prefix that fits its preview pane. Any part of the subject past the threshold is cut, so the important half has to be at the front.
The Formula
shown = the first T characters, where T is about 41 on a phone and 60 on a tablet
The client shows only the prefix that fits its preview pane. Any part of the subject past the threshold is cut, so the important half has to be at the front.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| s | Subject line | characters | The full text entered into the subject field. |
| T | Threshold | characters | How many characters the client shows before truncating. |
| L | Length | characters | How many characters the subject actually has. |
What Each Symbol Means
scharacters
Subject line
The full text entered into the subject field.
Tcharacters
Threshold
How many characters the client shows before truncating.
Lcharacters
Length
How many characters the subject actually has.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to write email subject lines page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Write Email Subject Lines, filed under Everyday Life. Every number the guide produces comes from substituting into this one line.