More than two million people watched Thursday night's football game between the Buffalo Bills and New York Jets for free on Twitter.

That was smaller than the digital audience Yahoo saw when it streamed an NFL game, also for free, last October (though Yahoo autoplayed that game on its homepage and most of its properties, including mail and Tumblr, so the comparison isn't clean at all). It’s also well below the 48.1 million who tuned in to watch the game on TV, according to Nielsen.

Here are more relevant numbers, if you really want to compare Twitter’s reach vs. traditional TV: An average of 243,000 people were watching the game on Twitter at any given time, while CBS and the NFL network, which simulcast the game, reached an average of 15.4 million.

No one expected Twitter to generate TV-level numbers, of course. Streaming the game digitally, for free, is still a big experiment for all parties involved.

But the audience total is a good benchmark to use for the NFL — and for Twitter investors — as the season plays out. Thursday’s game was the first of 10 games Twitter is set to stream for free over the next three months.

Twitter’s average audience number was calculated using a rating metric known as average minute audience, or the average number of viewers calculated per minute during the game. This is also how Nielsen analyzes data for TV ratings, so the numbers should be comparable.

That means Twitter's metrics are more TV-like than the all-over-the-map digital metrics for videos, like total streams (which Yahoo used last year). That’s a rarity, but it should become more common if the digital video guys want to get taken seriously.

What we still don’t know — and probably won’t know for some time — is whether these streams will generate any new users for Twitter. The company has just over 300 million total users, and hasn’t been growing much at all over the past year. The streaming deal with the NFL is a chance to change that by luring folks without Twitter accounts to the service with something they do like: NFL football.

But you don’t need a Twitter account to watch the NFL on Twitter, which means Twitter will need to find a way to convince visitors that it’s worth signing up for an account. The company isn’t breaking out how many of Thursday’s viewers were active users.