The _gcl_au cookie
A Google Ads cookie the Google tag's conversion linker sets on your own domain so ad clicks can be tied to conversions.
_gcl_au at a glance
- Cookie name
_gcl_au- Vendor
- Google Ads
- Category
- Advertising
- Party
- First-party
- Typical duration
- 90 days
- Set on
.<your-domain>- Value format
1.1.<random-number>.<timestamp>- Name match
- Exactly
_gcl_au
What the _gcl_au cookie does
_gcl_au is a first-party identifier that the Google tag, through its conversion linker, stores on the site's own domain. It lets Google Ads measure conversions and associate them with ad interactions without relying on third-party cookies. Google lists its purposes as analytics, advertising and security.
Google documents a 90 day lifetime, and Google tag settings can change the cookie prefix, domain and expiry. The 1.1.<random>.<timestamp> value structure is commonly observed but not documented by Google. It is one of several _gcl_ cookies; others such as _gcl_aw hold click details when a visitor arrives from an ad.
What TagPipes observed
13%
of sites scanned set it (5,174 of 41,162)
90 days
median observed lifetime
TagPipes scanned 41,162 public websites between August 11, 2026 and September 13, 2026, loading up to three pages per site in a real browser as a first-time visitor. _gcl_au was present on 5,174 of them.
It was set as a first-party cookie on 5,046 sites and as a third-party cookie on 255. A site can count in both. Where it was stored as a persistent cookie, the median lifetime we recorded was 90 days.
Often found alongside
Percentage of sites with _gcl_au where the other cookie was also present.
Technologies detected on the same sites
- Google Analytics on 99% of them (55% of all sites scanned)
- DoubleClick on 88% of them (11% of all sites scanned)
- Google Fonts on 86% of them (78% of all sites scanned)
- Google Tag Manager on 77% of them (30% of all sites scanned)
- Google Ads on 67% of them (12% of all sites scanned)
Aggregate figures across all sites scanned. Websites of TagPipes customers are excluded, no individual site is named, and cookie values are never read or stored. Snapshot dated September 13, 2026.
How to check for _gcl_au on a website
- Open the site in Chrome, then open DevTools (F12, or Cmd+Option+I on a Mac).
- Go to the Application tab and expand Cookies in the left panel.
- Select each domain listed there and look for
_gcl_au. The Expires column shows when it will be deleted. - If it is not there, reload the page. Many cookies are only set after a tag has loaded, and some only after a visitor has made a consent choice.
Sources
Purpose, duration and value format checked against the vendor documentation above on . The figures under What TagPipes observed are TagPipes scan data from September 13, 2026, not values documented by the vendor. Vendors change their cookies, and sites can configure their own names and lifetimes. Browse all cookies.
Know every cookie your own site sets
TagPipes Pulse identifies the cookies dropped on your site and flags unclassified or miscategorized ones. Shield builds your cookie declaration from a real scan rather than a questionnaire.
TagPipes monitors, configures and reports. It does not determine legal compliance and does not provide legal advice. Output is informational and reflects observed state at the time of observation. Rawsoft's expertise is technology, not law; please confirm any regulatory interpretation with your own counsel.