Good captions are not just correct. They are short enough to read, on screen long enough to finish, and broken in the right places. The rules below come from broadcast and accessibility guidelines that have been tested on millions of viewers, and then adapted to short vertical video, where the text is bigger and the screen is smaller.
If you want the clicks that apply these rules, read how to edit caption text and timing alongside this guide.
The short version
Keep lines short (the broadcast limit is 42 characters), show at most two lines, leave enough time to read (up to about 20 characters a second for adults), break lines at natural pauses, and caption the sounds that matter, not just the speech. On a phone, use even fewer words per screen.
What the professional guides say
The Netflix English timed-text style guide is one of the most detailed public rulebooks for subtitles. Its main numbers:
| Rule | Netflix English guide |
|---|---|
| Characters per line | 42 at most |
| Lines on screen | Two at most (one line unless the text is too long) |
| Reading speed, adult programmes | Up to 20 characters per second |
| Reading speed, children’s programmes | Up to 17 characters per second |
| Long pause in speech | A pause of two seconds or more can be shown with an ellipsis |
These figures are for television-size screens. Short vertical video is read on a phone, usually with larger, bolder text. Fewer characters fit on a line, so the practical limits are tighter. CapsField’s Caption Tools start at 22 characters per line on vertical videos and 24 on landscape ones, for that reason.
Rule 1: keep each line short
A line you cannot take in at a glance is a line people skip. Aim for a short phrase, not a whole sentence. In CapsField, open Caption Tools and use:
- Words to show 1 to 5 words per screen. Fast videos often work best at 2 or 3.
- Max chars to set the longest line before it breaks.
- Max lines to limit the text to one, two or three lines.
Fast-paced, punchy videos suit one to three words. Interviews and tutorials suit longer groups. Never fill the picture with text.
Rule 2: use one or two lines
The guide allows two lines at most, and a single line when the text fits. Three lines hide too much of the picture and are hard to read in one glance. If a thought needs more, split it into two captions that follow each other.
Rule 3: give people time to read
The reading-speed ceiling of 20 characters per second is the top end for adults, not the target. Short captions that stay on screen a little longer feel calm. Captions that flash by feel stressful. Practical rules:
- A very short caption (one or two words) should still be on screen for a moment, not a flicker.
- If you cut the pace of a video, check that captions still have time to be read.
- If speech is very fast, show fewer words per screen rather than packing them in.
You can fine-tune each caption’s start and end on the Lines row of the timeline. See the editing guide.
Rule 4: break lines where people pause
The Netflix guide gives clear advice for where to break a line:
- After punctuation.
- Before conjunctions such as and and but.
- Before prepositions such as in and with.
- Never between a noun and its article, a noun and its adjective, or a first name and a last name.
- Prefer a shape that is wider at the bottom, and avoid leaving only one or two words on the top line.
A caption that breaks mid-phrase makes the viewer’s brain do extra work. Read it aloud: if you would pause there, a break is fine.
Rule 5: write numbers, names and emphasis consistently
- Numbers: the Netflix guide spells out zero to ten and uses numerals for 11 and above, except for times, ages and some units. Whatever convention you choose, use it throughout the video.
- Names and brands: spell them the same way every time. Use Search & Replace in the editor to fix a spelling everywhere at once.
- Emphasis: make one word stand out at a time, not whole lines. In CapsField, Emphasize and Spotlight are in the word menu.
Rule 6: caption more than speech
Accessibility standards expect captions to carry the full audio picture. The W3C’s explanation of Success Criterion 1.2.2 (Captions, Prerecorded), a Level A requirement in WCAG 2.2, says captions should include spoken dialogue, identify who is speaking, and describe meaningful non-speech sounds. For a short vertical video you do not need to caption every noise, but if a sound changes the meaning (a phone ringing, laughter, a siren), consider adding it in brackets, for example [laughs].
The scale of the audience is real. The World Health Organization estimates that about 430 million people worldwide need rehabilitation for disabling hearing loss, and projects over 700 million by 2050. Many more people watch with the sound off by choice. Clear, well-timed captions serve both groups.
Rule 7: check contrast and position
The best timing cannot save text that cannot be seen. Use a bold typeface, strong contrast with the footage (a box or outline helps), and keep captions inside the app-safe area. The safe zone guide and the styling guide show how.
A quick checklist
- Lines are short (one idea each)
- No more than two lines at once
- Each caption stays long enough to read
- Lines break at natural pauses
- Names, numbers and punctuation are consistent
- Important sounds are captioned
- Text is high contrast and inside the safe zone
Frequently asked questions
How many characters should a caption line have?
Broadcast guides cap a line at 42 characters. For short vertical video, shorter lines of around 20 to 25 characters read more comfortably.
How many lines of captions should I show?
One or two. Three lines cover too much of the picture and are slow to read.
How fast can people read captions?
Netflix’s English guide sets a ceiling of 20 characters per second for adult programmes and 17 for children’s. Staying below that ceiling is more comfortable.
Do I have to follow Netflix’s rules?
No. They are a professional benchmark, not a law for your channel. They are useful because they were refined on a very large audience.
Are captions required by law?
Rules differ by country and by kind of content. WCAG, the standard many laws refer to, expects captions for recorded video with sound at its basic level. Check the rules that apply to you.
Put the rules to work
Start with one video. Create a free CapsField account, open Caption Tools and set Words, Max chars and Max lines to match the rules above. Then read the result aloud.
