Subtitles are on in more homes than ever, and in a lot of them they are hard to read: too small, lost against a bright scene, or gone before the sentence ends. Most of that is down to a handful of settings and one number worth knowing.
A 2021 survey commissioned by the charity Stagetext found that 80% of 18 to 24-year-olds use subtitles some or all of the time when watching TV, and a YouGov poll in 2023 put 61% of that age group down as preferring them on. A US survey of 1,265 people by Preply, reported by Fox, found 72% blamed muddled audio. If you also struggle to follow speech, our piece on why you can't hear the dialogue on your TV covers the sound side. This one is about the words on screen.
Professional subtitles follow written rules. Netflix publishes its own: no more than 42 characters per line, no more than two lines, white text, centred at the bottom or top of the picture, and for adult programmes a reading speed of up to 20 characters per second (17 for children's programmes). A subtitle stays up for at least five-sixths of a second and at most seven. Those figures come from Netflix's general requirements and its English style guide; other services and broadcasters set their own limits.
The same guide asks for lines to break after punctuation and before conjunctions, and not to split a name or an article from its noun. That is why a good two-line subtitle reads like a sentence and a bad one reads like a ransom note.
Pick a scene, a size, a backing and a line shape. The panel tells you what you gave up.
On a dark scene almost anything works. The trouble starts when the picture goes bright: snow, sky, a white wall. White text with no backing sinks into it, and a thin outline only helps a little. A semi-opaque box behind the text is the most reliable fix, and most streaming apps and TVs have a setting for it, often called background or edge style. Try Bright and Busy with each backing above and you will see the pattern.
Size matters second. Text that is comfortable on a phone is small from a sofa, and viewing distance is why: the further back you sit relative to the screen, the larger the text needs to be. Our piece on how big your screen should be works through that geometry. Make it larger until a full line fits across the picture without wrapping or running off the edge, which is also why the 42-character rule exists.
A subtitle that disappears before you finish it is a timing problem, not an eyesight one. The measure is characters per second: how many characters the line holds divided by how long it stays up. Try it below.
The marks are Netflix's two ceilings: 17 characters per second for children's programmes and 20 for adult ones. Crowded dialogue is where subtitlers have to cut words to stay under the line, which is one reason the text on screen can differ from what you hear. If a scene always outruns you, the fix is the pause button, not a better TV.
Streaming apps often keep their own subtitle style menu, separate from the TV's system caption settings, so check both. Raise the size until a full line fits across the picture, add a box or a strong edge, keep the white text, and leave the position at the bottom unless something on screen keeps colliding with it. Then watch one scene you know is bright and one that is dark.
Subtitle options depend on the app, the TV and the film, and availability varies by country, so check what your service offers for the title you are about to play.