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We have been using IPLEGENCE Database pro to get user timezone based on IP address. Here I have a few unusal time zone off sets. Which are listed below

  • EST+1
  • PST-2
  • PST-1
  • GMT+12.75

I am not sure what exactly above listed off sets.

Could some one please help me in converting the above time zones to UTC.

Thanks for your time.

Madhu Kudala
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2 Answers2

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Here is a list of time zones. EST is almost always (excepting for those DST overlaps) GMT-5. And GMT is either on UTC, or an hour off (again, DST). 

EST+1 = GMT-4
PST-2 = GMT-10
PST-1 = GMT-9

The best you can probably do, if you want to convert it to UTC, is to use the DateTime object.

aynber
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That is rather a strange way to denote time zones. My guess is that GMT+12:45 refers to the Chatham Islands. Not sure about the others, they could be anywhere.

IMHO, there are a few problems with this type of data:

  • Time zones are not fixed offsets. When the database refers to EST, they probably mean "US Eastern Time". But that could refer to -5 hours offset for Eastern Standard Time (EST), or -4 hours for Eastern Daylight Time (EDT). By calling it "EST" in the data, they are fixing it to -5, when in fact it might be -4. See "Time Zone != Offset" in the timezone tag wiki.

  • Time zone abbreviations can be ambiguous. For example, how do I know that "EST" really refers to USA's Eastern Standard Time (-5)? It might refer to Australia's Eastern Standard Time (+10). There is a list here, and you can see there are lots of time zones with the same abbreviation.

  • IP Geolocation is a "best guess", and does not have the kind of accuracy needed to determine time zone. The time zone in these databases may match the listed coordinates, but you have very little guarantee that the user is actually at those coordinates. It might be giving you the location of a proxy server or network router. This is especially true on corporate networks, where (in some cases) you have an IP in a corporate office in another city and all Internet traffic filters through that IP. You're going to get the timezone of that corporate office - not the time zone of the user. You can read more about IP Geolocation Accuracy here and here.

If you know the coordinates of the user by some other means, such as from GPS data on a cell phone, then you can use one of the several different techniques described here.

Community
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Matt Johnson-Pint
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  • Can you please suggest me that the better way to get user time zone in UTC format. Thank you. – Madhu Kudala Jul 01 '13 at 17:30
  • @MadhuKudala - I'm sorry, but that doesn't make sense. A *time zone* doesn't have a format, and UTC isn't a format anyway. If you are trying to get the time zone of your user, you will find the question has been asked many times before. Just search. – Matt Johnson-Pint Jul 01 '13 at 17:44