Nine hours a day is a lot of time to spend on something. It’s more than most people sleep at night. It’s how many hours a day many adults spend doing their job. And according to a new study by Common Sense Media, it’s the amount of time the average teenager spends using media each day.

The nonprofit group, which is “dedicated to helping kids thrive in a world of media and technology,” studied media habits of 2,600 tweens (defined as 8 to 12 year olds) and teens (defined as 13 to 18 year olds). They documented what kinds of media male and female tweens and teens used (like video games, social media, music), how long they spent on each type of media and what devices they used.

It’s a tricky — but important — thing to measure. Why? According to Common Sense Media:

“Media devices are portable, ubiquitous and integrated as essential tools in young people’s lives, and what counts as “media use” or even “screen time” is harder to define. It is no longer simple to define what “TV” or even “reading” is. And measuring how much time is spent on a particular activity is not straightforward either, since many media are used in short bursts throughout the day, while others may be on in the background all the time.”

Some of the study’s findings may give parents pause. For example, the average teen girl spends more than 90 minutes a day on social media, and the average teen boy spends one hour every day playing video games. Not good, considering studies link excessive screen time to attention problems, difficulty in school, sleep and eating disorders and obesity, according to the Mayo Clinic.

Related: Tips for Managing Screen Time That’s Out of Control

Where do kids find nine hours a day? They don't; they multitask, often using several forms of media at once.

“The fact that young people spend a certain amount of time each day with media does not mean that they spend that time doing nothing else but using media,” the study’s authors wrote. “If a teen spends an hour watching TV, an hour listening to music, an hour reading, and an hour using social media, she will have a total of four hours of media use. But … she may be doing other activities at the same time. For example, she may be watching TV while getting dressed or cleaning her room, browsing social media while on the bus to school, and listening to music while working out.”

Not all media use is bad, of course. Using the Internet to research a homework assignment, using a computer or smartphone to video chat with distant relatives or using an app to track fitness goals are all good ways to use media and technology.

The infographic below details more results of the study, and you can read the key findings here.

Related: Looking for Quality Children’s Television? Check Out These Shows

media use by tweens infographic(Photo: Common Sense Media/Common Sense Media)