Subtitling

The document that quietly became the industry’s shared definition of a well-made subtitle — and the exact numbers behind it. Netflix’s Timed Text Style Guide (TTSG) is one of the most detailed, publicly available subtitle specifications in the streaming industry, and it has become something close to a de facto standard well beyond Netflix’s own platform. Reading-speed limits, line-length rules, and timing conventions that originated in Netflix’s internal specification now show up, in close to identical form, across other streamers, YouTube style guides, and independent creators’ subtitle workflows — not because those platforms coordinated with Netflix, but because the guide represents some of the most rigorously tested public thinking on what makes a subtitle actually readable. This breakdown walks through what the TTSG actually requires — file format, reading speed, character limits, timing, positioning, and SDH — and explains why so much of it has been adopted well outside Netflix’s own delivery pipeline. Whether the goal is delivering to Netflix directly, or simply borrowing from the most tested subtitle standard available, understanding these rules in detail is useful for almost anyone producing subtitles professionally. Why Netflix’s Guide Became the Industry Benchmark Netflix publishes its Timed Text Style Guide openly through its Partner Help Center, broken into a general requirements document plus dozens of language-specific guides covering grammar, punctuation, and formality conventions unique to each language. That level of public detail and language-by-language granularity is unusual — most streaming platforms manage subtitle specifications through closed vendor relationships rather than a searchable public knowledge base — and it’s a major reason the TTSG gets referenced, adapted, and quoted well outside Netflix’s own vendor network. The guide is also unusually rigorous about the mechanics of readability specifically. Its reading-speed and timing figures didn’t emerge from guesswork; they reflect extensive testing on how quickly viewers can actually process on-screen text without falling behind or losing track of the picture. That’s the underlying reason so many of these numbers keep reappearing verbatim across other platforms’ specifications and independent style guides. File Format and Technical Requirements Netflix’s subtitle delivery format is built on TTML (Timed Text Markup Language), with strict rules about how styling is expressed inside the file. Two technical details stand out because they trip up files built for other platforms: For teams working across multiple delivery formats, not just Netflix’s, our SRT vs VTT vs ASS subtitle format guide is a useful companion to this section, since it covers how the more common general-purpose subtitle formats differ from the strict TTML-based delivery format Netflix specifically requires. Reading Speed and Timing Rules This is the part of the TTSG most frequently cited outside Netflix, because the numbers have become something close to an unofficial industry default: Rule Netflix Specification Maximum reading speed (adult content) Up to 17 characters per second (CPS) for most languages Maximum reading speed (kids’ content) Up to 13 CPS for most languages Minimum subtitle duration 5/6 of a second per event (e.g. 20 frames at 24fps) Maximum subtitle duration 7 seconds per event Minimum gap between subtitles 2 frames, to prevent consecutive subtitles from appearing to flash or blur together Line count One line preferred; two lines only when needed to stay within the character limit Files that exceed these thresholds get flagged automatically during Netflix’s quality-control process, before a human reviewer ever looks at the content — meaning a technically accurate translation with a reading-speed violation still fails delivery. The standard fix for a CPS violation is to split the line or trim the wording, not to speed up the timing, since compressing the display duration further only makes the reading-speed problem worse. Character Limits and Segmentation Netflix’s 42-character-per-line limit is probably the single most widely copied number from the entire guide — it shows up, often unchanged, in YouTube’s own subtitle recommendations and in countless independent creator style guides. Text should generally be kept to one line unless it exceeds that limit, and when a line does need to break into two, segmentation has to happen at a clause level so each line reads as a complete, logically self-contained thought rather than an arbitrary word-count split. For subtitles split across two consecutive events because a sentence continues, timing and punctuation both follow specific rules: ellipses are generally not used when the pause between the two parts is under two seconds, but are used when the pause is longer or when dialogue trails off. Netflix additionally specifies the single smart ellipsis character (U+2026) rather than three separate periods — a small detail, but one that automated QC checks for directly. Punctuation Conventions Differ Even Within English One detail that surprises people encountering the TTSG for the first time: Netflix maintains separate style guides for different English variants, and they don’t always agree with each other. US English uses double hyphens to indicate an abrupt interruption by another speaker or a sudden sound; UK English uses an ellipsis for the same situation instead of hyphens. Getting this backward — using US conventions on a UK-English delivery, or vice versa — is exactly the kind of detail that looks like a stylistic quirk but is actually a hard specification difference that automated and human QC both check for. This regional specificity extends throughout the guide: each language-specific TTSG covers its own conventions for quotation marks, italics, numbers, currency, and formality — currency mentioned in dialogue, for instance, is kept in its original currency rather than converted, regardless of the target language. Positioning Rules Subtitles are required to be center-justified and placed at either the top or bottom of the screen — Netflix doesn’t support left- or right-aligned subtitle blocks for standard delivery. The one documented exception is Japanese content, where vertical positioning is permitted under Netflix’s Japanese-specific Timed Text Style Guide, reflecting the vertical reading conventions native to the language. When on-screen text (like a sign or a letter shown in the frame) overlaps with spoken dialogue, Netflix’s guidance is to prioritize whichever message is more plot-pertinent, and specifically warns