Facebook Vs Twitter
Graphic by author.

With about 1.5 billion monthly active users, Facebook (NASDAQ:FB) is the undisputed king of social networks. Its audience represents more than half of the entire global Internet population including China -- which it's locked out of by censorship laws. Twitter (NYSE:TWTR), comparatively, has just more than 300 million monthly active users that log into its social network.

But Twitter CFO Anthony Noto argues that Twitter's total audience is much bigger than that number. Facebook only has "the 1.4 billion they report; there's no other number," Noto told the audience at the Deutsche Bank 2015 Technology Brokers Conference in mid-September. "We have other audience numbers that no one talks about, and when you add those up, it's a big number. In fact, in some scenarios you could argue that it's bigger."

Bigger than Facebook?
Throughout last year, Twitter tried to emphasize the extent of its total audience beyond its active users that log in. Former CEO Dick Costolo told investors that the audience on its owned-and-operated properties was two to three times the size of its active users. That doesn't include the audience it gets through syndication in news stories and other apps.

In November, the company gave additional details, noting that more than 500 million visitors come to Twitter every month without logging in. Additionally, it said it saw 185 billion tweet impressions through syndication. Noto laid out a long-term forecast for where the company could be if it effectively monetized those audiences. At the conference, he admitted that Twitter is behind where he expected it to be at this point.

In the long run, Noto believes the total audience represents an $11 billion incremental opportunity. That doesn't include Vine, which has 100 million monthly active users, and Periscope, with its 10 million registered users. Combine those with Twitter's visiting audience and syndication, and Noto is right that its total audience may be comparable to Facebook's 1.5 billion monthly active users.

Still, even fully monetized, Twitter's total audience doesn't compare to Facebook's revenue. Analysts expect Facebook to top $17 billion in sales this year, speaking to the engagement Facebook is able to obtain from its audience. While the audience size might be one thing, its value ultimately comes from how many ads they're looking at and clicking on. That's something that gets harder as users move further away from the core Twitter user experience.

And what about all of Facebook's other properties?
Noto conveniently ignores Facebook's other properties when making the comparison between Twitter's total audience and Facebook's. Instagram has more than 400 million users, and WhatsApp has more than 900 million active users. Messenger has more than 700 million monthly active users, and Facebook recently started allowing people to sign up without a Facebook account.

While most of Instagram's users are also on Facebook, Pew estimates about 6% of Instagram users don't use Facebook. That's about 24 million. WhatsApp, meanwhile, has an audience that is much more complementary to Facebook's existing audience. With 900 million active users, it likely adds significant reach to Facebook's audience.

What's more, Facebook has made its ecosystem of apps work well together. An increase in Instagram use can lead to higher engagement of users on Facebook, as users cross-post on both platforms. Using the Facebook app can lead to more use of its Messenger app, and vice versa. Most of Facebook's other apps drive more traffic and content to its flagship platform, as well. WhatsApp, however, still stands on its own as a largely separate entity.

Twitter has been working to integrate its three main properties more closely. Users have always been able to insert Vines in their timelines, and many use Twitter to announce they'll be on Periscope in the near future. Still, there's room to further integrate these properties with its flagship platform to drive more users to all three properties.

When accounting for all of Facebook's and Twitter's properties, it's very doubtful that Twitter's audience is actually bigger than Facebook's. Even if it is, Twitter's potential to monetize its sizable audience is well below Facebook's, with its highly engaged audience.

Nonetheless, there are several areas where Twitter can improve engagement and grow its audience, which could lead to additional ad revenue. Ultimately, however, Twitter ought to shed the comparisons between itself and Facebook, and focus on making the most of the audience that it does have.

Adam Levy has no position in any stocks mentioned. The Motley Fool owns and recommends Facebook and Twitter. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.