In a world where there are so many metrics available, there’s often a curious shortage of figures in some parts of the tech industry where you’d like there to be. Amazon won’t tell you how many Kindles its sold. Netflix won’t say how many episodes of House of Cards it has streamed. And so on.

So it’s interesting to read today that Apple has said that it has delivered over 5m downloads or streams of Serial so far. This is the fastest ever podcast to reach that number. But what does that really say?

Well so far there have been 8 episodes of Serial, so if everyone who used iTunes to listen to Serial, dutifully listened to each episode, that’d mean 625,000 downloads of each episode.

In reality, I suspect that the first episode has been delivered more than any other. Despite it being “the Breaking Bad of radio,” not everyone will get on with it and might drop out after a handful of episodes.

Here’s a possible breakdown of listening by episode based on nothing more than random guesswork taking that thesis into account:

One way or another, I expect the chart would look more like this than a fist line.

This does of course ignore the fact that once subscribed, you might not unsubscribe and just ignore podcasts piling up on your device. They still get credited as a download.

But unfortunately, in the scheme of things, we don’t really know what this all means. While Serial has been sitting at the top of the US and UK iTunes podcast chart for the last couple of months, that doesn’t really tell you anything.

iTunes tries to keep its podcast charts dynamic. If it didn’t, then the top performers would fill the slots repeatedly. So it’s never a question of just how many podcasts have been downloaded over a given time period, but they inject some secret sauce into their formula that almost certainly looks at the rate of growth of a particular podcast, and factor that in too.

And it’s important to note that not all podcasts are delivered via iTunes. You can stream many podcasts direct from the websites of those podcasts, and if you’re using a phone – particularly a non-iPhone – there are any number of podcast apps that you might use to download your listening. Stitcher is one popular one. I currently use Pocket Casts on Android for my own listening. But there are many others.

Depending on your own set-up, if you have your own podcast, you might be able to get your analytics software to determine where your audience is coming from. iTunes is almost certainly the biggest single delivery mechanism, but others are important too, even if cumulatively.

But how does your podcast compare with others out there? Well that’s where you run into difficulties. Certainly you can look at the iTunes podcast charts, but they’re flawed as I’ve mentioned.

Now however, you can look to see whether your last eight podcasts have delivered 5 million downloads or streams via iTunes. If they have then congratulations – your podcast is as big as Serial. Why haven’t I read about it in the weekend broadsheet press?

And if your last eight podcasts were delivered 50,000 times in total by iTunes, then congratulations – your podcasts is 1% the size Serial. We do at least have a comparator!