Open Google Analytics 4, click the Admin gear icon in the bottom left, then navigate to Data Streams under the Property column. Click on your website's data stream (usually named after your domain), and you'll see the Measurement ID displayed prominently at the top right of the stream details screen. It starts with "G-" followed by 10 alphanumeric characters, like G-ABC123DEF4. If you manage multiple properties or streams, make sure you're in the correct GA4 property first. The property selector is at the top of the Admin panel. Each data stream gets its own Measurement ID, so if you have separate streams for staging and production environments, they'll have different IDs. Don't confuse this with the older Universal Analytics tracking ID (UA-XXXXXXXX-X), which is deprecated and won't work with GA4. You can also find the Measurement ID in the Google tag itself if it's already installed on your site. View your page source and search for "G-" to locate it in the gtag.js script. This is useful when auditing a site you didn't set up yourself. At Ottawa SEO, we typically store Measurement IDs in a documentation sheet for each client in our 500+ domain portfolio, alongside GTM container IDs and Search Console property URLs. This prevents the scramble when a developer needs it during a site migration or redesign. We've seen too many projects stall for 20 minutes while someone with admin access hunts down credentials. One tradeoff: GA4 lets you use the same Measurement ID across multiple domains if you're tracking a funnel that spans sites (like a main site and a separate checkout domain). But for most businesses, one ID per distinct property keeps reporting clean. If you can't access Admin, you don't have sufficient permissions on that GA4 property. You need at least Editor role to view data stream settings. Ask the property owner to grant access or provide the ID directly.