Method to calculate time spent in meetings

I just got a request from my boss asking if there's a way to sum up how much time people here spend in meetings. Has anyone here been asked about something like this? I know this is a first for me. One thing that helps is that the vast majority of meetings take place in one of three conference rooms. In order to schedule a meeting there, it has to be approved and and goes in a calendar for that room. Is there a way to aggregate that data into a file or something?