How long should a caption be, and how fast?

By the maker of Captions Cut. Facts checked on 22 October 2026 from the pages listed under Sources.

The short answer

For landscape video, the common rules are up to 42 characters per line and two lines (Netflix) at up to 20 characters a second for adults. For vertical 9:16 video, the BBC’s equivalent is about 25 characters per line across 90% of the width, up to three lines, at 160 to 180 words a minute. Word-by-word captions show fewer words at once, which keeps lines short by design.

The guidelines

Guideline	Line length	Lines	Speed	Timing
BBC Subtitle Guidelines	37 characters (broadcast); ≈ 25 characters across 90% of a vertical 9:16 frame	2 for 16:9 and 1:1; up to 3 for 9:16	160–180 words a minute	At least about 0.3 s per word
Netflix (English, USA)	42 characters	2	Up to 20 characters a second (17 for children’s)	—
DCMP Captioning Key	—	2	130–160 words a minute for educational media, by level	At least 1⅓ s, at most 6 s

What changes in vertical video

The frame is narrow, so lines must be shorter: the BBC equates 37 characters across 75% of a landscape frame with about 25 across 90% of a vertical one, and allows a third line. The app’s own buttons also take the edges and bottom, which pushes captions toward the middle (see safe zones).

Word-by-word captions

Captions that highlight each word as it is spoken let the eye follow the voice, and the short lines suit the narrow frame. In Captions Cut, each style sets how many words and lines appear at once, and in the iPhone app you can split or merge lines when a phrase reads better together.

Questions

How many words per caption is best?

The guidelines count characters, not words: about 25 characters a line in vertical video, 37 to 42 in landscape. For short-form clips, two to five words at a time reads easily.

Sources

Each page read on 22 October 2026.

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