Determine the time zone you wish to convert the time from (see worldtimezone.com, for example). Take into account Daylight Saving Time when determining time zone, as daylight time will add an hour to the local time and decrease the number of hours you must add during the conversion process. For a western hemisphere location, we will use Pacific Standard Time as an example.
Refer to a time conversion table such as the one at iris.edu (see References) in order to determine the number of hours to add. Note that UTC conversion tables are designed to convert UTC into local time. Therefore, in order to convert local time to UTC, reverse the process described in a UTC conversion table, adding hours instead of subtracting.
For example, when converting local time in the Pacific Standard time zone to coordinated universal time, a UTC conversion table shows that eight hours must be subtracted when converting UTC into Pacific Standard Time, designated at the left side of the table as "-8." Therefore, in order to convert Pacific Standard Time to UTC, you add eight hours to the local time, converting 2:41 p.m. into 10:41 p.m.
Note that if you were using Pacific Daylight Time, you would only add seven hours to compensate for the hour added by daylight time.
Write the adjusted local time in 24-hour format. For times before noon, add a zero in front of the previous three digits. Times after noon are expressed from 13:00 to 23:00, instead of 1:00 p.m. to 11:00 p.m. Therefore, 2:41 p.m. is written as 14:41 when expressed in a 24-hour format, or as 22:41 when adjusted for the Pacific Standard time zone in step two.
Remove the colon from the time displayed. UTC is written as four digits without a separating colon. Therefore, 2:41 p.m. in the Pacific Standard time zone converts to 2241 in UTC.
Determine the time zone you will use when converting local time into UTC. Be sure to account for Daylight Saving Time when determining the time zone, as it will add an hour to local time and increase the number of hours to subtract when converting to UTC. For this example, we will use the Central European time zone.
Refer to a UTC time conversion table in order to determine the number of hours to subtract when converting local time to UTC. Remember that UTC time conversion tables are designed to convert UTC into local time, meaning that you must reverse the process described on the table. In this case, Central European Time is described as being one hour ahead (+1) from UTC. Therefore, in order to convert local time to UTC, an hour must be subtracted, making 2:41 p.m. 1:41 p.m.
Note that if you were using Middle European Summer Time you would need to subtract two hours from local time in order to account for the hour added by daylight time.
Convert the adjusted local time figure into a 24-hour format. For times before noon, add a zero in front of the previous three digits. Times after noon are expressed from 13:00 to 23:00, instead of 1:00 p.m. to 11:00 p.m. As 1:41 p.m. takes place after noon, the time would be converted to 13:41 p.m.
Remove the colon from the displayed time. UTC time figures do not include any sort of separating punctuation between the four digits. When completed, 2:41 p.m. in the Central European time zone converts to 1341 in UTC.
