Captions for Shorts, Reels and TikTok: size, placement and accessibility

Who uses captions?

More people than you might think. The BBC Subtitle Guidelines say around 10% of broadcast viewers use subtitles regularly, rising to 35% for some online content, and that most of those viewers aren’t hard of hearing. Captions are also an accessibility basic: the W3C’s WCAG 2.2 success criterion 1.2.2 (Level A) asks for captions for all prerecorded audio in video.

Burned-in or closed captions?

Burned-in (open) captions are part of the picture. They show on every platform and every device, and nobody has to switch them on. WCAG lists open captions as one way to meet success criterion 1.2.2. They can’t be turned off or resized, so make them readable from the start.
Closed captions are a separate text track that viewers turn on or off. YouTube, Instagram and LinkedIn all offer them (see below).

For short clips posted to several platforms, burned-in captions are the simplest way to make sure everyone sees them. If you burn them in, check whether the platform is also adding automatic captions, so viewers don’t see two sets on top of each other.

What good captions include

WCAG says captions should cover not just the dialogue but who is speaking and meaningful sounds, such as laughter or music that matters to the meaning. Leaving out dialogue is listed as a failure. In practice:

Caption every spoken word that matters. The BBC prefers verbatim captions where the reading speed allows.
If two people talk, make it clear who is speaking, for example with a different colour for each speaker.
Label important sounds, such as [laughter] or [music].
Check spelling, names and numbers. Automatic captions make mistakes.

Readable sizes for 9:16 video

The BBC guidelines are written for TV and iPlayer subtitles, but they include specific advice for vertical 9:16 video, which makes them a useful benchmark for social clips:

Text height: a line height of 3.9% to 4.5% of the video height, for example 4.2%. On a 1920-pixel-tall video, that’s roughly 75 to 86 pixels per line.
Line length: up to 90% of the frame width, which the BBC suggests works out at about 25 characters per line as a guide.
Lines: no more than three at once.
Safe area: keep text within the central 75% of the height and 90% of the width.
Contrast: the BBC uses white text on a black background for legibility. Whatever style you choose, make sure the text stands out from every frame behind it.

Where to place captions

For 9:16 video, the BBC suggests placing subtitles a little higher than the bottom of the frame but still in the lower third, as faces are usually in the top half. On social platforms this matters even more, because the app’s buttons, usernames and post text sit along the bottom and sides.

Meta’s safe zone guidance for 9:16 Reels and Stories ads says to keep the top, bottom and side edges free of key text and logos, and to use large, contrasting text. For Reels ads with disclaimers, it says to leave the bottom 40% free.
TikTok’s ad specifications note that the safe zone depends on the video dimensions and the length of the post caption.
LinkedIn’s video help also advises keeping the edges clear.
Never cover the speaker’s mouth, an on-screen name or anything the viewer needs to read.

Timing and reading speed

The BBC’s guideline reading speed is 160 to 180 words per minute, with a minimum of about 0.3 seconds per word.
Break lines at natural points in the sentence, not in the middle of a phrase.
Keep captions in sync with the speech. Word-by-word highlighting is a popular style for Shorts, as long as each word stays on screen long enough to read.

Each platform’s caption tools

YouTube: automatic captions are available for long videos and Shorts, including in English. YouTube says quality varies and that you should always review them, which you can do in YouTube Studio under Subtitles. They may not be ready straight after upload, and can fail with poor audio, overlapping speakers or a long silence at the start.
Instagram: captions can be generated automatically by speech recognition, but may not be available to everyone. Add them before sharing with the Captions sticker, or afterwards by editing the post and turning on closed captions under Advanced settings. Instagram says captions show automatically unless they’re turned off, which is worth knowing if your captions are already burned in. Instagram also lets you add alt text to a Reel.
LinkedIn: auto-captions are available in 10 languages, or you can upload your own caption file.

Quick checklist

Every spoken word that matters is captioned and spell-checked
Speakers are distinguishable and key sounds are labelled
Text height about 4% of the frame height (75–86 px at 1920 tall)
No more than three lines, about 25 characters per line
Placed in the lower third, clear of platform buttons and faces
High contrast against every frame
Reading speed no faster than about 180 words per minute
No double captions from platform auto-captions

FAQ

Should I burn captions in or use the platform’s captions?

For clips posted to several platforms, burned-in captions are the simplest way to make sure everyone sees them. Platform captions can be switched on or off by viewers but aren’t available everywhere. If you burn captions in, check the platform isn’t adding a second set automatically.

How big should captions be on a vertical video?

The BBC Subtitle Guidelines suggest a line height of 3.9% to 4.5% of the video height for 9:16 video. On a 1080×1920 clip that’s roughly 75 to 86 pixels per line.

Where should captions go on Shorts and Reels?

In the lower third but not right at the bottom, clear of the platform’s buttons and post text, and not over faces. The BBC suggests a little higher than the bottom of the frame for 9:16 video.

Are YouTube’s automatic captions good enough?

YouTube says automatic caption quality varies and recommends always reviewing them. You can edit them in YouTube Studio under Subtitles.

What do captions need to include for accessibility?

WCAG says captions should include the dialogue, who is speaking, and meaningful sounds. Leaving out dialogue is listed as a failure.

Official sources

Platform features change often. Check the sources above before you publish.

Captions for short-form video: size, placement and accessibility