A survey by comScore found Americans spent an average of 7 hours, 21 minutes, accessing Facebook on smartphones in March, compared with 6 hours, 31 minutes, from computers, ZDNet.com reported Tuesday.
Facebook accounts for most of smartphone users' time, the survey found, with other social networking sites like Foursquare, Twitter, Tumblr and LinkedIn far behind.
The closest was Foursquare, with 141 minutes average usage in March.
"Social networking proved to be a particularly popular activity on smartphones with several brands demonstrating exceptionally high engagement, in some cases higher than the corresponding time spent by users via traditional Web access," comScore said in a statement.
Facebook has more than 901 million monthly active users and more than 488 million mobile monthly active users, comScore reported.