SAN FRANCISCO Wed Apr 9, 2014 2:52pm EDT

(Reuters) - Facebook Inc said on Wednesday it is switching to fewer but bigger ads on the right-hand column of the desktop PC version of its website because users respond more frequently to them.

The new right-hand display ads will be the same proportions as the so-called News Feed ads, which inject paid marketing messages straight into a user's stream of news and content. That will make advertising on Facebook simpler for marketers, since they will no longer need to use different images for different types of ads, Facebook said in a post on its Facebook for Business blog.

In tests of the new ad design, Facebook said it has seen up to three times more user "engagement" with the ads. The company did not provide specifics, but typically the term means some kind of user interaction such as clicking on the ad, posting a comment or resharing it.

Facebook did not specify how many ads will now appear in the right-hand column, though a sample image on the blog showed a single ad in the right-hand column. The company previously displayed as many as seven box-like display ads in the right hand column.

Facebook, which has more than 1.2 billion users, said some advertisers will begin seeing the new option later this month. The changes affect only the PC version of Facebook's website, which now accounts for less than half of its ad revenue as Facebook users and marketers increasingly favor the mobile version of its service.

(Reporting by Alexei Oreskovic; Editing by Cynthia Osterman)