“How long should a Reel be” is the most asked and least useful question in short-form. It gets answered with a number, the number gets repeated until it sounds like policy, and creators end up padding or truncating videos to hit a duration that was never the mechanism.
Length is a proxy, and a poor one
Since Mosseri's remarks in early 2025, watch time has been widely reported as the heaviest ranking signal across Instagram's surfaces, alongside likes per reach and sends per reach. Note what that measures: time, not percentage and not duration.
Which means length only matters through its effect on time watched, and it pushes in two directions at once. A longer video has more time available to accumulate. A longer video also has more opportunities to lose the viewer. The optimum is wherever those two stop trading favourably, and that point is set by your material, not by a rule.
A short video watched three times and a long video watched most of the way through can produce the same number. They are not the same skill.
What this implies in practice
Two videos can arrive at identical watch time by opposite routes. A tight 15-second piece that loops cleanly accrues time through repetition. A 60-second piece that holds three quarters of its audience accrues it through duration. Both are legitimate; they demand different things.
The looping route needs an ending that rejoins the beginning without a seam, and it needs the video to be short enough that a second viewing feels free. The duration route needs structure — a reason to still be there at forty seconds that was not the reason at ten.
The rule that survives
There is exactly one length rule worth keeping: the video should be as long as its material and not one beat longer. That sounds like a platitude until you apply it as an edit rather than an aspiration.
Take the finished cut and remove everything that is not doing work — the restatement, the wind-down, the sign-off, the pause before the real point. What remains is the length. If that number is eleven seconds, the video is eleven seconds. Padding it to hit a target adds exactly the material most likely to lose people.
Why longer Reels being allowed is not an instruction
Instagram has raised its Reels ceiling repeatedly, and each increase produces a wave of advice to make longer videos. The ceiling is a permission, not a recommendation. It tells you what is now possible to upload; it says nothing about what will be watched.
The signal to watch is your own: does your audience's watch-through hold as your videos get longer, measured against your own baseline rather than against a published benchmark? If it holds, you have room. If it does not, the ceiling is irrelevant to you.
The question worth asking instead
Not “how long should this be” but “where does this lose people, and is that loss necessary?” Those are answerable from retention, and the answers change what you cut rather than how long you aim for. For which numbers actually answer that, see seven metrics that beat view count.