There are 25 time zones around the globe, each spanning approximately 15 degrees of longitude, although the lines are not straight--in some areas, they jog to accommodate political boundaries. The starting point for the time zones is Greenwich Mean Time, where the Prime Meridian passes through Greenwich, England. Eastern Time (EST or EDT) covers most of the east side of the United States and Canada, from Connecticut to Indiana. Pacific Time (PST or PDT) covers the West Coast of North America, including California, Nevada, parts of Idaho and the Yukon.
Determine whether the region in question is observing Pacific Standard Time or Pacific Daylight Time. PST is used in winter. PDT is used in summer during Daylight Saving Time.
Find out the current time. For example, say it is 12:30 a.m. PDT in Los Angeles.
Add three hours to get EDT. For example, 12:30 a.m. in PDT will be 3:30 a.m. EDT in Indianapolis.
To convert back to PDT, subtract three hours from EDT. If it is 6 p.m. EDT in Indianapolis, it will be 3 p.m. PDT in Los Angeles.