When it comes to PPV buy rates we never really get disclosed true and accurate figures. However the one reliable and lone source for UFC pay-per-view figures has and always will be, Mr. Dave Meltzer.
When people talk of buys, stating this PPV did this amount and this one did that, it is all based on his industry intelligence. The UFC never confirms figures, nor do the broadcasters, however, Meltzer’s time in the PPV business has gone on way before the UFC existed and therefore his estimates and contacts are widely considered as valid and on point.
With that being said, here is what he said via MMAFighting.com about UFC 173:
UFC 173, which featured T.J. Dillashaw’s upset bantamweight title win over Renan Barao, is estimated at doing between 200,000 and 215,000 buys on pay-per-view based on a variety of independent sources.
The number is about what would have been expected given the industry trends and neither main event fighter having strong name recognition. Most likely, the co-main event, where Daniel Cormier submitted Dan Henderson to put himself into the light heavyweight title mix, had the most interest of any fight coming into the show.