UTCHowto

UTC Howto

What is UTC?

Coordinated Universal Time (UTC) is the official world time. Localized times can be calculated through addition or subtraction to the current UTC time. For most timezones, this conversion uses integer multiples of hours (i.e. +1:00, +2:00, -3:00, etc). Typical dates in UTC can look like these:

2007-06-07 04:00 UTC
2007-06-07 04:00 +0000
2007-06-07T04:00UTC

You can find a long article about UTC at Wikipedia.

How can I convert UTC into local time?

There are several ways:

1. Do mental arithmetic. You need to know the offset of your timezone and add it to the current UTC time. A table with some time zone offsets is presented below.
2. You can use the command line tool date for this. This conversion only works when you use a machine that is configured to display your time zone.

   $ date -d '2007-06-07 04:00 UTC'

   This would print:

   Thu Jun  7 00:00:00 EDT 2007

   for someone using Eastern Daylight Time.
3. You can use an online time calculator.

How can I convert my/any local time into UTC?

1. Do mental arithmetic. You only need to subtract the offset of your timezone from your local time to get UTC. A table with some time zone offsets is presented below.
2. You can use the commandline tool date for this conversion.
   1. You can use the -d option to provide a date to convert:

      $ date -u -d "2007-06-07 00:00 EDT" +"%Y-%m-%d %H:%M %Z" 

      Yields the converted time in UTC:

      2007-06-07 04:06 UTC

   2. Ignore the -d option to use the current system time.

      $ date -u +"%Y-%m-%d %H:%m %Z"

      Yield the current converted time in UTC:

      2007-06-29 20:06 UTC

3. You can use the graphical tool international-time:

   $ international-time

4. You can use an online time calculator.

Table of time zones

A very complete, albeit somewhat intimidating list of time zones listed by their UTC conversion factor can be found on Wikipedia. They use the convention UTC+X to sort the zones (UTC equals the GMT). If you lived in New York, for example, you would look under UTC-5, during summer (EDT) you would look under UTC-4. If you liven in Berlin using CET, you would look under UTC+1, or UTC+2 in the summer.

GMT	UK/Greenwich Mean Time	London	0000	2015-06-07 04:00 GMT
EST	US/Eastern Standard Time	New York	-0500	2015-06-07 00:00 EST
EDT	US/Eastern Daylight Time	New York	-0400	2015-06-07 00:00 EDT
CET	Central European Time	Berlin	+0100	2015-06-07 05:00 CET
CEST	Central European Summer Time	Berlin	+0200	2015-06-07 05:00 CEST
BST	UK/British Summer Time	London	+0100	2015-06-07 05:00 GMT