Good question. And of course that all depends on the sitcom and the story.
In general, sitcoms filmed in studios in front of an audience have fewer than those filmed with a single camera for a variety of practical and tonal reasons. A studio sitcom is more like a play, and for that reason, scenes tend to run longer, and play out in real time, without tricksy editing or cheating jump cuts that you can use in a single-camera show.
Moreover, you can't keep setting up thirty scenes in one evening in front of an audience. It’s just not practical. There's not enough time on the night. But that’s okay. The audience subconsciously expect studio audience shows to have fewer scenes. And it will. If you have a main plot - with about 8-10 beats, you'll probably need a new scene for each of those beats. If you have a subplot with 5-6 beats, you might need separate scenes for some of those beats, but you might also have those plot developments taking place in the same scene as your main plot. And you might need an extra scene to pay of a C-Plot, which is essentially a running joke. So overall, it's unlikely you'd have fewer than eight scenes in a normal studio sitcom episode. And you might have as may as 16-18, depending on whether you have a couple of pre-shot scenes on location.
So conventionally, you’d probably have somewhere between 8 and 18 scenes for a studio sitcom. For me, 11-16 seems about right.
You might have that number of scenes for a non-audience single camera show too. But you could have much shorter, snappier scenes if you wanted. Maybe as many as thirty. I shudder to think how many scenes the writers of Modern Family cram into their 21 minutes, servicing over a dozen characters with three plots.
Of course, you can make a virtue of having only one scene in the whole show which plays out in real time. We did that on the psychiatrist episode on Miranda. It’s quite common for a sitcom to do that sort of thing on its second or third series for a bit of variety. It’s normally called a ‘bottle’ episode, in which the characters are all trapped or marooned somewhere and it’s quite talky, but often quite revealing in terms of characters. This is when sitcoms become most ‘play-like’. Writers love the challenge of writing them. Audiences could, I suspect, take them or leave them. If they don’t find it as funny as normal, they won’t give you points for trying to be clever. (Critics will, but who cares what they think? They're being paid to watch TV and then write something clever about it. Most people watch comedy because they like laughing.) More on 'Bottle Eps' here.
But it’s not just studio audiences who try to run everything in real time. Some single camera shows like to do this. I seem to remember Roger and Val Have Just Got In did every episode this way, with each episode being set just after work when Roger and Val, er, get in. There's more on this play/film/real-time tradition here.
Again, critics and industry-types go mad for hyper-realism or real time. My own view is that the audience really just like laughing – and if these kind of tricks make it funnier, so be it. But they normally just make it harder to get laughs. So as a rule, I would suggest this ‘one scene episode’ thing should be approached with great caution. Stick to your 11-16 scenes to give yourself the best chance.