Tag ID, Measurement ID, Destination ID

How are these different? What do they mean? Where do you use them?

Hands up if you remember setting up a Universal Analytics tag? I know it's been a while, but you must recall adding the tag id - UA-12345-1 or something similar yes?

GA4 is a little different. In our last post, we made reference to a recent change from Google regarding the automatic firing of a gtag for Google Ads and Floodlights if one didn't exist. Here's a gtag example:

The gtag has a Tag ID.

Here's a GA4 Event:

The GA4 tag has a Measurement ID.

A GA4 data stream has a Measurement ID, And they appear to be the same value:

But a Tag ID can be different to a measurement ID, and you can't use a Tag ID in a GA4 Event, you have to use a measurement ID.

But which is which and WHY? This can be confusing - understandable.

Delving into the GA4 Data stream, we can click on the "Configure tag settings" option in the google tag section:

OOh, look - interestingly, our Google tag has two IDs. Click it:

Confirmed: TWO TAG IDS. Below this, you'll see "Destinations":

Notice the Destination ID is the Stream Measurement ID. The Measurement ID acts as both the unique identifier for the data stream and the destination ID ensuring data collected by the tag is routed to the correct GA4 property.

So what?

You can't use a Tag ID in a GA4 Event - it's not a measurement ID. GA4 Tags use Measurement IDs.

You can generally use the Measurement ID in a gtag, and a GA4 tag, as long as you've confirmed they're both valid Tag IDs - this isn't 100% guaranteed. Tags and destinations can be remapped, or deleted,

This is worth mentioning if you haven't noticed there's a difference. It might save your data