We all know that YouTube is pretty popular these days, but do you have any idea just how popular it is? That’s hard to quantify of course, but let’s just say that if the latest estimation of over four billion hours of YouTube videos being watched each and every month is at all accurate, it gets a whole LOT of air time.

For those too lazy to do the math, that equates to something like 456,000 years of YouTube vids and user-uploaded content being watched every 30 days. Or, it’s the same as one person sitting there and watching the original Nyan Cat video no less than 66 billion times.

The news was first reported earlier this week, getting the briefest of mentions in an article in the Wall Street Journal on Monday. Although YouTube’s official site stats have not been updated to reflect the latest figures, the company has apparently confirmed the new figure as being correct in an interview with Mashable.

What this shows is that there is seemingly no end to YouTube’s popularity – just a few weeks ago, in May, the company revealed that ‘only’ 3 billion hours of content was being streamed by viewers each month – which means in the last month and a half, the amount of footage viewed on YouTube has increased by a staggering 25%.

It looks as if YouTube’s investments are paying off. Although YouTube is best known and loved for its user-uploaded content, the company has recently begun developing a number of ‘professional’ channels. Effectively, YouTube seems to be transitioning into a broadcaster of sorts, having diverted over $150 million into channels featuring stars like Wayne Brady and Amy Pohler. At the time of its last viewing figure announcement, YouTube said that it planned to splurge another $200 million in order to set up more channels like these.

No doubt, YouTube will soon be celebrating the day when we’re watching five billion hours each month.