How Long Should a Video Ad Be? The Platforms Disagree
One recommends under 15 seconds with no data. One recommends 15 to 30 for placement eligibility, not attention. The two with the most data say nothing.
Two of the four largest video advertising platforms refuse to recommend a duration at all. One of the two that does cites nothing. The other gives its reason openly, and the reason is placement eligibility, not attention.
That asymmetry is the most useful thing on this subject. The platforms holding the deepest video measurement in the industry have declined to publish a number, and the ones publishing numbers are not showing their work.
This page sets out what each platform actually says, what constrains your length in practice, and how to decide.
What each platform publishes
Read the official pages and the picture is not a consensus with edge cases. It is a genuine split.
The largest social platform recommends, without evidence. Its guidance says feed video ads can run up to 60 minutes, but that shorter videos under 15 seconds tend to perform best in feed, and that stories ads perform best under 10 seconds. Elsewhere it says shorter videos of 6 to 15 seconds are more effective, and that shorter is better but context matters. No study, no sample, no period appears alongside any of it.
The professional network recommends, and says why. It recommends uploading videos 15 to 30 seconds long, so they can qualify for all possible placements across its feed and its audience network. That is a stated, checkable, technical reason. It is also not a claim about how long people watch.
The video platform declines. Its creative effectiveness playbook, the flagship document on what makes video advertising work, contains zero occurrences of the words length, duration or shorter, and no reference to 15 or 30 second formats. It publishes format maxima only.
The short-video platform declines too. Its creative best practices page gives hook timing and nothing about overall duration. Its in-feed specification page states a ten minute limit for standard ads and no restriction for the boosted-post format, with no recommendation attached.
What that pattern means. The two organizations with the most video advertising measurement in existence have looked at this question and published nothing. That is a finding, and it should lower your confidence in anyone who has published a number.
The professional network’s guidance is the only one you can act on with confidence, and not for the reason people assume.
What it says. Upload videos 15 to 30 seconds long so they can qualify for all possible placements across the feed and the audience network.
What that is. An eligibility constraint. Certain placements will not accept your video outside that window, so a video outside it reaches a smaller inventory pool.
What it is not. Evidence that 15 to 30 seconds holds attention better. The platform does not claim that, and reading it that way turns a technical fact into a folk belief.
Why this is still the most useful number on the page. Because you can verify it, it does not depend on anyone’s study, and it has a direct consequence: a 45-second video competes in fewer auctions.
The general principle to take from it. Your practical duration window is usually decided by which placements you want to be eligible for. Work out the placements first, then take the intersection of their limits, then write to that.
The limits that actually bind
The specification pages vary far more than the recommendations do, and they are hard constraints rather than advice.
Desktop in-stream: 5 to 15 seconds. The same placement on mobile allows 5 seconds to 10 minutes. One placement, two device contexts, and a fortyfold difference in ceiling.
Stories: 1 to 120 seconds on the largest social platform.
Rewarded video: 3 to 61 seconds on its audience network.
Non-skippable in-stream: 60 seconds or shorter on the video platform.
Bumper: between 5 and 6 seconds, non-skippable, on the same platform.
Skippable in-stream: no maximum, with under 3 minutes recommended.
Professional network: 3 seconds to 30 minutes. An extremely wide window whose practical range is narrowed by the eligibility rule above, not by the specification.
Short-video platform: up to 10 minutes for standard in-feed ads, no restriction for the boosted-post format.
What to do with this. Write down the placements you want, list their windows, and take the intersection. That is your real duration constraint, and it is knowable without any research.
One placement can cap at 15 seconds on desktop and allow ten minutes on mobile. Work from the intersection of what you want to run. Source : Platform specification pages, read directly (2026)
The measurement problem underneath short video
One platform mechanic quietly makes short-video reporting incomparable, and almost nobody accounts for it.
The mechanic. On the professional network, videos under 30 seconds loop until there are at least 30 seconds of playback. A 10-second video loops three times. A 20-second video loops twice. Videos over 30 seconds play once.
What that does to completion. A short video accumulates completions from repeat plays that a longer video cannot. Its completion rate is not measuring the same event.
What that does to watch time. Average watch time on a short video there includes looped seconds, so a short video can report watch time approaching its longer competitor while showing the viewer the same eight seconds four times.
Why this interacts with the eligibility rule. The platform recommends 15 to 30 seconds, and 15 to 29 seconds is precisely the range that loops. The recommended range is the one where the metrics are hardest to read.
What to do. Never compare completion rates between a video under 30 seconds and one over it on that platform. Compare cost per outcome, which does not care how many times the file played.
And keep the general lesson. Before believing any duration comparison, check whether the two durations were measured on the same basis. Frequently they were not.
The one measurement that exists, and it complicates the case for short
There is a single open, sampled study of skip behaviour, and its central finding is proportional rather than absolute.
The study. HTTP traces from a campus network, March to November 2014, 99,658 video-ad exhibitions across 5,667 unique ads, desktop only.
The headline numbers. 29% of exhibitions were watched in full. 35% were skipped in under six seconds. Only 25% ran past ten seconds before the viewer skipped.
The finding that matters here. On average, a user skipped after 20% of the ad content had been shown, with a standard deviation of 19%.
Why that is awkward for the short-video argument. If departure is proportional to length rather than fixed in seconds, then a longer ad receives more absolute seconds of exposure, not fewer. Twenty percent of 60 seconds is twelve seconds. Twenty percent of 15 seconds is three.
The caveats that stop this becoming a rule. The study did not test length as a variable, so the proportionality could be an artefact of the ad mix rather than of viewer behaviour. It is 2014 desktop, skippable in-stream only. And the standard deviation is nearly as large as the mean, so there is no typical viewer to design for.
What it does establish. That the intuition behind short video, that people bail at a fixed number of seconds, is not what the one available measurement found. That is enough to justify testing a longer version rather than assuming it will fail.
There is one place where a platform does publish duration performance, and it deserves a specific warning.
What it claims. A platform blog states that video ads falling between 21 and 34 seconds received a 280% lift in conversion. The same page claims a 312% lift for videos shot at 720p or higher, 91% for the 9:16 aspect ratio, and 152% for text-format calls to action.
What the page contains in support. No footnote. No source. No sample size. No period. No description of the comparison group. No definition of lift.
Why the numbers themselves should worry you. A 312% conversion lift attributable to resolution is not a plausible creative effect. It is far more likely a selection artefact: advertisers who shoot at higher resolution differ from those who do not in every other respect too.
What the other platform’s unsourced figures look like. The largest social platform states that feed video ads perform significantly better with sound on, at 2.25x higher call-to-action click-through rate, and that 98% of users hold their phones vertically. Same pattern: specific figure, no source.
How to use any of this. As a statement of what the platform wants you to do. That is genuinely informative, because platforms optimise for their own inventory and their preferences are real. It is not evidence.
The test that settles it for you. Two lengths, same message, same audience, running concurrently. A week of spend beats every unsourced multiple in the category.
A 312% conversion lift from resolution is not a creative effect. It is a selection artefact with a percentage sign. Source : Platform creative blog, read directly (2026)
How to actually decide
Six steps, none of which requires anybody to have published a threshold.
List the placements you want. Not the ones available. The ones you intend to run.
Take the intersection of their duration windows. That gives you a hard range, and it is often narrower than you expected.
Write to the message, not to the range. Inside the window, length should follow what the message needs. An ad that fills 30 seconds because 30 was allowed is worse than one that finishes at 12.
Front-load regardless of length. Departure begins immediately in a feed, so a 40-second ad and a 10-second ad have the same first four seconds problem.
Test two lengths concurrently. Same message, same audience, same landing page, running at the same time rather than one after the other.
Judge on cost per meeting held. Not on completion rate, which as shown above is not comparable across the 30-second boundary on at least one platform.
Two of the four largest video platforms publish no duration recommendation at all, including the one with the deepest creative measurement in the industry.
The platform recommending under 15 seconds cites nothing. No study, no sample, no period.
The professional network’s 15 to 30 seconds is an eligibility rule, stated as such: videos in that range qualify for all possible placements.
The real constraints are placement specifications, and they vary far more: 5 to 15 seconds on desktop in-stream, 5 seconds to 10 minutes on the same placement on mobile.
Videos under 30 seconds loop on the professional network until 30 seconds of playback accumulates, so completion rates across that boundary are not comparable.
The recommended 15 to 30 second range is precisely the range that loops, which makes it the range where metrics are hardest to read.
The platform lift figures have no methodology. A 312% conversion lift attributed to recording resolution is a selection artefact, not a creative effect.
Decide from your placements and your message, then test two lengths concurrently and judge on cost per meeting held.
No platform has published measurement supporting an answer. Two recommend a range and cite nothing, one of them for a reason unrelated to performance. The two platforms with the most video data decline to recommend at all.
Why does the professional network say 15 to 30 seconds?
It says why, and the reason is technical: videos in that range qualify for all possible placements across its feed and audience network. It is an eligibility rule, not a claim about attention.
Does the largest video platform recommend a length?
No. Its creative effectiveness playbook contains zero occurrences of length, duration or shorter. It publishes format maxima only: 60 seconds for non-skippable, 5 to 6 seconds for bumper, and under 3 minutes recommended for skippable.
What about the 21 to 34 second figure?
It appears on a platform blog claiming a 280% conversion lift for that range, alongside several other lift figures. The page carries no sample size, no period and no methodology. Treat it as a platform position, not as data.
What actually constrains my length?
Placement specifications, far more than attention. Desktop in-stream caps at 15 seconds while the same placement on mobile allows ten minutes. Rewarded video runs 3 to 61 seconds. Bumper is 5 to 6. Those are hard limits.
Why do my short videos show strange completion rates?
On the professional network, videos under 30 seconds loop until at least 30 seconds of playback accumulates. A 10-second video loops three times. Completion and watch-time figures for short videos there are counting repeats.
Should I just make everything short?
Short is a reasonable default because departure begins immediately in a feed. But the honest reason is that people leave, not that a platform published a threshold. Length should follow what the message needs.
How do I decide for my own account?
Pick the placements you actually want, take the intersection of their duration limits, and test two lengths inside that window on the same audience, judged on cost per meeting held.