Explanation of Cookie Values Used by Google Analytics 4

Table of Contents

Update time: Dec 17, 2024

The following first-party cookies are generated and used in GA4:

Cookie name	Default expiration time	Description
_ga	2 years	Used to distinguish users.
_ga_<container-id>	2 years	Used to persist session state.
FPID	2 years	Used to distinguish users.
FPLC	20 hours	Used to cross-site tracking

Note：Although the default validity period is 2 years, the actual validity period is 13 months. This is because there is an industry rule in current browsers that the validity period of first-party cookies is 400 days, which is about 13 months. Therefore, the validity period you see in the cookie is about 13 months.

Next, let me introduce the specific information in these two cookies, take bbccss.com as an example:

_ga

By default, GA4 assigns a unique Client ID to each device as a unique user, which is stored in the browser’s cookie _ga. The structure of _ga is as follows:

Note: 1197596843.1673515099 is the Client ID.

The detailed explanation is as follows:

Value	Description
GA1	Version number, which represents the version of the cookie format that’s being used.
1	Domain Level, In fact, GA4 generates all 1.
1197596843	Random Number, 10 digits
1673515099	Timestamp, the timestamp when cookie _ga was created

_ga_<container-id>

The structure of _ga_<container-id> is as follows:

The detailed explanation is as follows:

Value	Description
GS1	Fixed String: Google Stream 1
1	Domain Level, In fact, GA4 generates all 1.
1673933110	Session ID/Current Session Start Time
12	Sessions Count
0	Engagement Session, 1 means engagement session, 0 means no
1673933110	Current Timestamp
60	Countdown，60-second countdown may be used to calculate the Engagement Session or the time spent on the page.
0	to be determined
0	Enhanced Client Id, abbreviated as ecid, is a string of numbers that only has value when tracked on the server side tracking.

For the first request of the session, the Session ID and Current Timestamp are the same, because the Session ID is the Current Session Start Time

FPID

The full name of FPID is First-party device IDs, which is set through server-side tracking. Therefore, it is only available in server-side tracking：

This cookie is httponly, and the variables in GTM cannot obtain it.

The value of FPID is as follows:

FPID2.2.F99Fd7gVuQuP93MZdJiEn07o/eZba6j9bAt8ETLsn8E=.1733280703

Note: F99Fd7gVuQuP93MZdJiEn07o/eZba6j9bAt8ETLsn8E=.1733280703 is also called Client ID

Value	Description
FPID2.2	Version number
F99Fd7gVuQuP93MZdJiEn07o	TBD
eZba6j9bAt8ETLsn8E=	TBD
1733280703	Timestamp

FPLC

You may also see Cookie FPLC.

Since FPID is HttpOnly, GTM cannot read it, so FPID cannot achieve cross-site tracking.

FPLC is used to solve the problem that FPID cannot be tracked across sites.

FPLC is the hash value of the FPID cookie. It is not HttpOnly, which means that JavaScript can access FPLC and use it for cross-domain tracking.

FPLC is valid for only 20 hours.

Referral：

Cross-Domain Tracking on Google Analytics 4 (GA4)

If you don't understand, You can leave a comment below.

_ga

_ga_<container-id>

FPID

FPLC

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