The six second rule states that a subtitle should never be on screen for more than 6 seconds. 6 seconds is supposed to be the maximum amount of time it takes for most adults to read a subtitle. Keeping it on screen for longer would cover up the video unnecessarily and annoy the viewer.

While everyone’s reading speed can be different, there is an unspoken rule that says that a subtitle should not be on screen for less than 1.5 seconds, in order to make sure that most people have time to read it before moving on to the next line.

The standard size for subtitles tends to be around 22 points, but this is a convention more than a hard rule. It all depends on your font, background choices and the size/aspect ratio of your video. You need to experiment to see what works best for your content. In general, a good rule of thumb is to never have subtitles that are too small to read quickly, or so big that they become the main focus of your frame.

Captioning best practices dictate that a subtitle should not have more than two lines on screen at the same time. Additionally, a line should be no longer than 42 characters at a time to ensure that viewers can read the subtitle in time.

Each subtitle format comes with its own benefits and downsides. The best one depends on your situation, however, for general usage, SRT or VTT are the most widely-recognized ones, ensuring the best compatibility with online video sharing platforms and different video players.