GA4 Custom Dimensions and Metrics

GA4 Custom Dimensions and Metrics

Expert guidance for registering event parameters as custom dimensions and creating custom metrics.

Overview

Custom dimensions and metrics transform event parameters into reportable fields in GA4. All custom parameters remain invisible in reports until registered. Registration requires understanding scope types, following naming conventions, and accounting for processing delays.

Understanding Scopes

GA4 uses three scopes that determine what data the parameter applies to:

Event Scope

Applies to: Single event occurrence Lifespan: That specific event only Use for: Event-specific information

gtag('event', 'button_click', {
  'button_name': 'Subscribe',        // Event-scoped
  'button_location': 'header',       // Event-scoped
  'button_id': 'btn_subscribe_01'    // Event-scoped
});

Examples: form_name, video_title, button_name, page_section

User Scope

Applies to: All events from that user Lifespan: Session persistence (until cleared) Use for: User attributes that persist

gtag('set', 'user_properties', {
  'subscription_tier': 'premium',         // User-scoped
  'customer_lifetime_value': 5000,        // User-scoped
  'preferred_language': 'en'              // User-scoped
});

Examples: subscription_tier, customer_segment, company_size, signup_date

Item Scope

Applies to: Individual items in ecommerce events Lifespan: That transaction only Use for: Product-specific information

gtag('event', 'purchase', {
  'items': [
    {
      'item_id': 'SKU_123',
      'item_name': 'Blue T-Shirt',
      'item_color': 'blue',         // Item-scoped
      'item_size': 'large',         // Item-scoped
      'supplier': 'Vendor A'        // Item-scoped
    }
  ]
});

Examples: item_color, item_size, supplier, product_quality

Scope Selection Matrix

Dimension Limits

Standard GA4

GA4 360

Registration Workflow

Step 1: Send Parameter in Event

First, ensure the parameter is being sent in events:

Event-scoped parameter:

gtag('event', 'video_watched', {
  'video_title': 'Getting Started Guide',
  'video_duration': 180,
  'video_quality': 'hd'
});

User-scoped parameter (user property):

gtag('set', 'user_properties', {
  'customer_segment': 'enterprise',
  'subscription_tier': 'premium'
});

Item-scoped parameter:

gtag('event', 'purchase', {
  'items': [{
    'item_id': 'SKU_123',
    'supplier': 'Vendor A'  // Custom item parameter
  }]
});

Step 2: Verify in DebugView

Before registration, confirm the parameter appears:

1. Admin -> DebugView
2. Enable Google Analytics Debugger extension
3. Trigger the event
4. Click event in DebugView
5. See parameter in event details
6. Note exact parameter name (case-sensitive)

Step 3: Register as Custom Dimension

Navigate to Admin -> Data Display -> Custom Definitions:

1. Click "Create custom dimension"
2. Fill form:
   • Dimension name: Human-friendly name (e.g., "Video Quality")
   • Scope: Select Event, User, or Item
   • Description: Optional notes
   • Event parameter / User property: Exact name from code (case-sensitive)
3. Click Save

Step 4: Wait for Data Population

Critical: Custom dimensions don't appear immediately.

• Wait time: 24-48 hours
• Historical data: Retroactively processed
• New data: Starts populating
• Do not create duplicate dimensions while waiting

Step 5: Use in Reports

After 24-48 hours:

• Standard Reports: Add as secondary dimension
• Explorations: Select from dimension picker
• Filters/Segments: Filter by dimension values
• Google Ads: Export for audience building

Creating Custom Metrics

Standard Custom Metrics

For numerical tracking beyond standard metrics:

gtag('event', 'video_watched', {
  'video_title': 'GA4 Tutorial',
  'minutes_watched': 45,      // Custom metric
  'completion_rate': 85       // Custom metric
});

Registration:

1. Admin -> Data Display -> Custom Definitions
2. Click "Create custom metric"
3. Fill form:
   • Metric name: Display name (e.g., "Minutes Watched")
   • Scope: Event (only option)
   • Event parameter: Parameter name (minutes_watched)
   • Unit of measurement: Standard, Currency, Distance, Time (optional)
4. Save and wait 24-48 hours

Calculated Metrics

Create metrics derived from existing metrics:

Examples:

• Revenue per User = revenue / users
• Conversion Rate = conversions / sessions * 100
• Average Order Value = revenue / purchases

Creation:

1. Admin -> Data Display -> Custom Definitions
2. Click "Create custom metric"
3. Metric Name: "Revenue per User"
4. Type: Calculated
5. Formula: revenue / users
6. Save (no processing delay for calculated metrics)

Common Registration Examples

Event-Scoped Dimensions

User-Scoped Dimensions

Item-Scoped Dimensions

Troubleshooting

Dimension Not Appearing After 48 Hours

Possible causes:

• Parameter name mismatch (case-sensitive)
• Events not sending parameter
• Wrong scope selected
• Low data volume (threshold not met)

Solutions:

1. Verify exact parameter name in DebugView
2. Confirm events are sending parameter
3. Check scope matches how parameter is sent
4. Wait for more data volume

Parameter in DebugView But Not Reports

Expected behaviour for first 24-48 hours

If persists:

1. Check Realtime reports (available sooner)
2. Verify at least 1000 events with parameter
3. Check data retention settings
4. Confirm dimension registered correctly

Dimension Quota Exceeded

Cause: Hit maximum dimension limit

Solutions:

1. Delete unused dimensions
2. Combine similar dimensions
3. Plan essential dimensions
4. Consider GA4 360 for higher limits

Multiple Users Same Dimension Value

For user-scoped: Expected - applies to all user events For event-scoped: Expected if same value sent For item-scoped: Expected across products

Best Practices

Planning Strategy

1. Audit existing parameters - What are you already sending?
2. Prioritise dimensions - Which are essential for reporting?
3. Reserve capacity - Don't use all 50 immediately
4. Document dimensions - Maintain registry of all dimensions

Naming Conventions

Parameter names:

• snake_case
• Under 40 characters
• Descriptive and consistent

Dimension display names:

• Title Case
• Clear and descriptive
• Match parameter purpose

Documentation Template

## Custom Dimension: Video Title

**Parameter Name:** video_title
**Scope:** Event
**Description:** Title of video watched by user
**Events Using:** video_start, video_complete, video_progress
**Registration Date:** 2024-01-15
**Status:** Active

**Example Value:** "Getting Started with GA4"

**Reports Using:**
- Video Performance Exploration
- Content Engagement Dashboard

Quick Reference

Registration Checklist

• Parameter sent in events
• Verified in DebugView
• Correct scope selected
• Exact parameter name used
• Waited 24-48 hours
• Tested in Explorations

Scope Quick Guide

Limits Summary