Translated copy rarely keeps its length. In an ad that matters more than anywhere else: the headline sits in a fixed box, the button has a fixed width, and the voiceover has to end when the shot ends.
This article gives the numbers we use in our studio to plan for that, for 24 languages, and what to do with them.
Why expansion matters in ads
An article can grow by a paragraph and nobody notices. An ad cannot:
- Headlines are set large in a fixed area. A third more text means a smaller font or another line.
- Buttons and badges have a fixed width. “Shop now” becomes “Jetzt kaufen” or “Comprar ahora”.
- Subtitles have a maximum line length and a reading speed. Longer text needs more time on screen.
- Voiceover has to fit the edit. A line that takes longer to say than the original pushes past the cut.
Expansion by language
These are the planning ranges our studio uses to warn when a language will be tight, expressed as the length of the translation compared with the same message in English. A value of 1.20 means 20 percent longer.
| Language | Length vs English | Note |
|---|---|---|
| German | 1.20 to 1.35 | Compound words break subtitle lines early |
| Spanish | 1.20 to 1.25 | Fast natural delivery absorbs some of it in voiceover |
| French | 1.15 to 1.25 | |
| Italian | 1.15 to 1.20 | |
| Portuguese | 1.15 to 1.20 | |
| Romanian | 1.15 to 1.20 | |
| Dutch | 1.10 to 1.20 | |
| Greek | 1.10 to 1.20 | |
| Irish | 1.10 to 1.20 | |
| Bulgarian | 1.10 to 1.15 | |
| Polish | 1.05 to 1.15 | |
| Hungarian | 1.05 to 1.15 | |
| Latvian | 1.05 to 1.15 | |
| Lithuanian | 1.05 to 1.15 | |
| Maltese | 1.05 to 1.15 | |
| Czech | 1.05 to 1.10 | |
| Slovak | 1.05 to 1.10 | |
| Estonian | 1.00 to 1.10 | |
| Croatian | 0.95 to 1.10 | |
| Slovenian | 0.95 to 1.10 | |
| Serbian | 0.95 to 1.10 | Latin and Cyrillic both work |
| Swedish | 0.95 to 1.05 | |
| Danish | 0.90 to 1.05 | |
| Finnish | 0.90 to 1.05 | Fewer words, much longer words |
Two patterns stand out. The Romance languages and German run long. The Nordic and South Slavic languages barely change, though Finnish and German share the same practical problem: very long single words that cannot be broken where you would like.
Speaking rate: the limit for voiceover
For a dub, the question is not how many characters fit in a box but how many can be spoken in the time the original line took. We measured this on the voiceovers our pipeline produced, excluding lines with URLs, acronyms or numbers, which are spoken differently:
| Language | Characters per second | Lines measured |
|---|---|---|
| Spanish | 14.9 | 18 |
| Hungarian | 14.6 | 22 |
| German | 14.3 | 54 |
| Italian | 13.7 | 7 |
| Croatian (Natural voice) | 13.3 | 32 |
| French | 13.2 | 4 |
| Slovenian (Natural voice) | 12.1 | 54 |
| Serbian | 12.0 | 4 |
The French, Serbian and Italian figures rest on small samples, so treat them as indicative. The pattern is clearer than any single number: none of the languages we measured was spoken faster than 15 characters a second, and the gap between Romance and Germanic languages that people often assume did not show up.
How to budget a line
A simple rule follows from those rates:
Character budget = line duration in seconds × characters per second.
At 14 characters a second, a 2-second line holds about 28 characters and a 4-second line about 56. If the translation is longer than the budget, shorten the wording rather than speeding up the voice. Fast speech sounds rushed, and it is harder to follow in a language the viewer is hearing in an ad, not choosing to listen to.
The same budget works for subtitles: a viewer needs time to read a line, and the same 12 to 15 characters a second is a sensible ceiling.
Design for the longest language
You can avoid most expansion problems when you design the original ad:
- Leave room. Size headline areas for about a third more text than the English needs.
- Keep calls to action short. One or two words in English leave room for three in German.
- Avoid text in tight shapes. Copy inside badges, circles or speech bubbles breaks first.
- Let lines wrap. A layout that allows a second line handles long words better than one that shrinks the font.
- Leave pauses in the voiceover. A script with breathing room between lines gives every language space to fit.
How Ad Localizer handles it
When you translate an image ad, the translation review shows each translated text block in place, with flags, and you can edit any line that runs long. For video, the studio warns before you generate when a language will be tight against the original timing, and budgets each translated line from the speaking rates above, so the dub fits the edit.
Method and caveats
The expansion ranges are planning ranges, not averages from a published corpus. We use them to warn about tight fits and refine them from finished jobs. The speaking rates come from voiceovers our pipeline synthesized: 139 lines across seven languages measured on 3 September 2026, with Slovenian and Croatian measured again on the Natural voice on 12 October 2026. Your own copy, voice and pace will vary, so use these numbers to plan and your preview to decide.
For the full list of languages we support, see the languages page.