GA4 Custom Dimensions and Metrics: Setup and Use Cases

What Custom Dimensions Are For

GA4 custom dimensions let you capture and report on data that is specific to your business — things that Google's standard dimensions do not cover. Examples: customer subscription tier, product category, content author, experiment variant, or user role. Without custom dimensions, this data is invisible in GA4 reports even if you send it as event parameters.

How GA4 Custom Dimensions Work

Custom dimensions in GA4 require two steps:

1. Send the parameter with an event: your event must include the parameter as a property. For example: gtag('event', 'purchase', {plan_tier: 'enterprise', revenue: 499})
2. Register the custom dimension: in GA4 Admin, create a custom dimension that maps to the parameter name. Until you do this, the parameter arrives in GA4 but is not available in reports.

Types of Custom Dimensions

Event-scoped dimensions: associated with a specific event. For example, content_category on a page_view event, or plan_tier on a purchase event.

User-scoped dimensions: associated with a user and persisted across all their events. For example, user_type: "subscriber" or customer_segment: "enterprise". Once set, this dimension applies to all future events from that user.

Setting Up a Custom Dimension

1. GA4 Admin then Custom Definitions (under Data Display)
2. Click "Create custom dimension"
3. Dimension name: what you want to see in reports (e.g. "Plan Tier")
4. Scope: Event (for event-level data) or User (for user-level data)
5. Description: optional but helpful for your team
6. Event parameter: the exact parameter name from your event code (e.g. "plan_tier") — case-sensitive
7. Click Save

Registration takes up to 24-48 hours to appear in reports. Data sent before registration is not retroactively populated.

Custom Metrics

Similar to custom dimensions, custom metrics let you track numerical event parameters as reportable metrics. Examples:

• video_watch_time: seconds of video watched
• quiz_score: a user's score on an interactive quiz
• items_in_cart: number of items when checkout started

Create them in Admin then Custom Definitions then Custom Metrics. Choose the measurement unit (Standard, Currency, Distance, Time) to format the metric correctly in reports.

GA4 Custom Dimension Limits

• 50 event-scoped custom dimensions per property
• 25 user-scoped custom dimensions per property
• GA4 360 (paid): 125 event-scoped, 100 user-scoped

This limit means you cannot register every parameter you send — only the ones you actually need to filter and segment by in reports. Parameters you send but do not register are still collected in the raw data (BigQuery export) but not available for report segmentation.

Practical Use Cases

• SaaS businesses: plan_tier (free/pro/enterprise) as user-scoped dimension to segment all metrics by customer tier
• Ecommerce: product_brand, product_category as event-scoped dimensions on purchase events
• Content publishers: content_author, content_category, article_word_count as event-scoped on page_view
• B2B lead gen: company_size, industry, lead_source as user-scoped from form fields
• A/B testing: experiment_id, experiment_variant as event-scoped to measure test performance in GA4

Summary

Custom dimensions transform GA4 from a general analytics tool into a business-specific measurement platform. Register only the dimensions you will actively report on (to stay within the 50-dimension limit), send parameters consistently with every relevant event, and document your custom dimension schema so your team knows what is being tracked and why.

See our GA4 Setup & Audit service for custom dimension implementation.

Need custom GA4 tracking for your business? Contact Adslytics.