A straight answer
Short enough that people finish it. For most Australian small businesses that means 15 to 45 seconds, and the reason why matters more than the number.
If you want one answer and no lecture: aim for 15 to 45 seconds. Under 15 seconds when you are trying to be discovered by people who have never heard of you. Around 30 seconds for most day to day business posts. Up to 45 when you are genuinely explaining something, like a treatment, a process or what a job actually costs.
Now the reason, because it is the part that lets you make the call yourself next time. Instagram does not measure your video in seconds. It measures what proportion of it people watched, and whether they watched it twice. A 12 second reel that people finish beats a 60 second reel that people abandon at 20 seconds, even though the second one was technically watched for longer.
Length is not the thing being judged. Completion is. Length is just the easiest lever you have to control it.
This is where generic advice falls over. "Keep it short" is fine until you are a physio trying to explain what a first appointment involves, and you cannot do that in nine seconds without sounding like an ad. Pick the length that fits the job the video is doing.
Owners obsess over total length and ignore the only part that is genuinely make or break. People do not decide to leave at the 30 second mark. They decide in the first two, before your logo animation has finished, before you have said "hi guys," before the title card clears.
So the practical version of the length question is this: can someone tell what this video is and who it is for within two seconds? If yes, you have earned the rest of your runtime. If no, the length is irrelevant because nobody got there. That is the same reason a title slate at the start is one of the most expensive mistakes a small business makes on video.
Almost every time an owner asks whether a reel can be longer, the honest answer is that the video is trying to do too many jobs at once. Three tips, a bit about the team, the opening hours and an offer, all in one clip. That is four reels wearing a trenchcoat.
Splitting it is better on every axis. You get four chances to be discovered instead of one. You get four pieces of content instead of one, which quietly solves a large part of the how often should I post problem. And each one holds attention far better, because each one has a single point. If you are short on ideas to split into, there is a list of reel ideas for small business that works for most trades and services.
The one genuine exception is a story. A real before and after, a build, a rescue, a transformation with a payoff at the end. People will stay for a story well past 45 seconds because they want to know how it ends. Nobody stays that long for a list.
General advice gets you to a sensible starting point. Your own account tells you the rest, and it takes about a month to hear it. Post at a mix of lengths, then open the insights on each reel and look past the view count, which is the least useful number on the screen.
The two that matter are average watch time and the share of viewers who were not following you. If people are consistently dropping at 12 seconds, your reels want to be about 12 seconds long, whatever any guide says. If your non follower share is high on the short ones and collapses on the long ones, you have just been told exactly where your ceiling is, by the only audience whose opinion counts.
Do that once, write the number on a sticky note, and stop rereading articles about length. Ten cafes in the same street will land on ten slightly different numbers, and all of them will be right for that cafe. The same logic applies to turning that attention into actual enquiries, which is a separate craft covered in how to get more customers from Instagram.
Slightly, not dramatically. TikTok viewers have more patience for a longer clip when the payoff is obvious, so a 45 second video that feels stretched on Instagram can sit comfortably there. The mechanism underneath is the same on both, though. Completion drives distribution, and a video nobody finishes gets shown to nobody new.
In practice this means you do not need two edits. Cut for Instagram, which is the stricter of the two, and the same file will hold up on TikTok. Cutting for TikTok first and hoping it survives the move across is the version that tends to disappoint.
Trimming a bad reel does not make it a good one. If a video is not being watched, the length is usually the third problem, not the first. Ahead of it: a weak opening that gave nobody a reason to stay, and no clear point to the video at all. Reels being posted in bursts and then stopping for six weeks is another, and no runtime fixes that either.
If you are still deciding whether short video is even worth your time, the fuller version of that argument is in do reels actually work for a small business and why reels. Length only starts to matter once you are actually posting.
Make it as long as the idea needs, then cut the first three seconds and the last five. The opening seconds are almost always throat clearing, and the ending is almost always a sign off nobody watched. What survives that cut is usually the right length, and it is usually shorter than you thought.
If being on camera is the thing making your videos drag, that is a fixable problem too, and it is covered in reels without being on camera. Hands, work, product and space carry a short reel perfectly well.
Knowing a reel should be 30 seconds does not make the month's worth of them appear. A short questionnaire becomes a steady month of branded reels, cut to length, reviewed by a human, delivered ready to post.
See how it works See the version for trades, clinics, cafes or gyms, or compare the cost against hiring a videographer. Email hello@reelmonth.com.au.