Data Layers for GA4 Ecommerce Events Guide

Colin Differ

24 February 2025

When it comes to using Data Layers for Enhanced Ecommerce in Google Analytics 4 (GA4), we felt it needed a whole separate guide so we can really get into the details of it. This guide is going to talk about what Data Layers you will need to enable Enhanced Ecommerce, what each Data Layer does, and where to use them.

What are Data Layers?

A Data Layer is a JavaScript object used to pass information from your website into Google Tag Manager and then into GA4. This data is not visible to users but can be leveraged to track detailed ecommerce interactions.

Why are Data Layers important for GA4?

GA4 uses an event-based model, which means everything is tracked via events like view_item, add_to_cart, etc. These need to be passed correctly using a Data Layer structure that GA4 can interpret. Doing this properly enables accurate reporting and deep analysis through GA4 and BigQuery.

Understanding the items Array

Every GA4 ecommerce event shares a common structure: the items array. This array holds one or more product objects, and its structure remains consistent across events like view_item, add_to_cart, purchase, and others. GA4 expects the same parameter names across all events for proper attribution and reporting.

Here’s what a consistent items array might look like:

items: [{
  item_id: 'SKU_12345',
  item_name: 'Sample Product',
  item_brand: 'BrandName',
  item_category: 'CategoryName',
  item_variant: 'Size or Color',
  price: 29.99,
  quantity: 1,
  currency: 'GBP'
}]

Using the same structure ensures GA4 correctly joins up impressions, clicks, views, cart adds, and purchases into unified product journeys.

GA4 Ecommerce Parameter Reference

Parameter Required? Applies To Description
item_id Yes All ecommerce events Unique product identifier (SKU or ID). Required for matching across events.
item_name Yes All ecommerce events Name of the product.
item_brand No All The brand of the item.
item_category, item_category2 – item_category5 No All Hierarchical product categories from broadest to most specific.
item_variant No All Product variation (e.g. color, size).
price Yes (for monetised events) add_to_cart, purchase, etc. Price of the item.
quantity Yes (where applicable) add_to_cart, purchase, refund Number of items affected by the action.
coupon No purchase, add_to_cart, view_item Discount code applied to the order or item.
affiliation No purchase Store or partner affiliation where the sale occurred.
transaction_id Yes purchase, refund Unique ID for the transaction.
value Yes purchase Revenue for the entire transaction
shipping No purchase Shipping cost.
tax No purchase Tax amount.
currency Yes All monetary events Currency code in ISO 4217 format (e.g., GBP, USD, EUR). Required for revenue tracking.
index No view_item_list, select_item Position of the item in the list.
item_list_name No view_item_list, select_item The name of the list the item appeared in (e.g., “Homepage” or “Search Results”).
item_list_id No view_item_list, select_item A unique ID for the item list being displayed or interacted with.
promotion_id No view_promotion, select_promotion Identifier for an internal promotion banner.
promotion_name No view_promotion, select_promotion Name of the promotion.
creative_name No view_promotion, select_promotion Name of the creative or ad (e.g., “Banner 1”).
creative_slot No view_promotion, select_promotion Placement of the promotion on the page (e.g., “homepage_banner_top”).
shipping_tier No add_shipping_info User-selected shipping level (e.g., Free, Next Day).
payment_type No add_payment_info User-selected payment method (e.g., Visa, PayPal).

Ensure consistency for parameters like item_id, item_name, and currency across all ecommerce events. In GA4, consistency is key for attribution and funnel analysis.

The view_item_list Event

What is it? This event fires when a user sees a list of products (like a category or search results page). Each product shown should be listed in the data layer.

What does it do? It helps GA4 track product exposure in lists and surfaces list names, item positions, and CTR analysis via events.

Where does it go? Place this in the <head> of any product listing page, or fire it dynamically as more products appear on scroll.

dataLayer.push({
  event: 'view_item_list',
  ecommerce: {
    item_list_id: 'home_page',
    item_list_name: 'Homepage',
    items: [
      {
        item_id: '345678',
        item_name: 'Product 1',
        price: 10.99,
        item_brand: 'Propellernet',
        item_category: 'Shorts',
        item_variant: 'Blue',
        index: 1
      },
      {
        item_id: '456789',
        item_name: 'Product 2',
        price: 45.99,
        item_brand: 'Propellernet',
        item_category: 'Trousers',
        item_variant: 'Red',
        index: 2
      }
    ]
  }
});

The select_item Event

What is it? Fired when a user clicks or selects a product from a product list.

What does it do? GA4 uses this to calculate CTR on lists, tracking how many impressions turn into clicks.

Where does it go? Fire this event when a user interacts with a product in a list to visit its detail page.

dataLayer.push({
  event: 'select_item',
  ecommerce: {
    item_list_id: 'home_page',
    item_list_name: 'Homepage',
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      price: 10.99,
      item_brand: 'Propellernet',
      item_category: 'Shorts',
      item_variant: 'Blue',
      index: 1
    }]
  }
});

The view_item Event

What is it? Sent when a user lands on a product detail page.

What does it do? This allows GA4 to track how often users are interested enough to view a product in full detail.

Where does it go? Add this to your product page, ideally in the <head>, or trigger it on load.

dataLayer.push({
  event: 'view_item',
  ecommerce: {
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      price: 10.99,
      item_brand: 'Propellernet',
      item_category: 'Shorts',
      item_variant: 'Blue'
    }]
  }
});

The add_to_cart Event

What is it? Triggers when a product is added to the cart.

What does it do? GA4 uses this to measure intent-to-buy behaviour. It helps track how many product views and clicks convert into adds-to-cart.

Where does it go? Fire this on any click or action that successfully adds an item to the cart.

dataLayer.push({
  event: 'add_to_cart',
  ecommerce: {
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      price: 10.99,
      item_brand: 'Propellernet',
      item_category: 'Shorts',
      item_variant: 'Blue',
      quantity: 1
    }]
  }
});

The remove_from_cart Event

What is it? Triggered when a user removes a product from their cart.

What does it do? It tracks friction or indecision in the buying process and can inform on product performance and UX problems.

Where does it go? Fire it wherever a remove-from-cart interaction takes place.

dataLayer.push({
  event: 'remove_from_cart',
  ecommerce: {
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      price: 10.99,
      item_brand: 'Propellernet',
      item_category: 'Shorts',
      item_variant: 'Blue',
      quantity: 1
    }]
  }
});

The view_promotion Event

What is it? Sent when a user views an internal site promotion like a homepage banner or featured section.

What does it do? Enables GA4 to track the reach of internal marketing placements.

Where does it go? On page load for pages with promo slots (e.g., homepage banners).

dataLayer.push({
  event: 'view_promotion',
  ecommerce: {
    promotions: [{
      promotion_id: 'GA-Train-Apr-25',
      promotion_name: 'GA4 Training April 2025',
      creative_name: 'Banner 1',
      creative_slot: 'Homepage Banner'
    }]
  }
});

The select_promotion Event

What is it? Fired when a user clicks an internal promotion (e.g. a banner).

What does it do? Lets GA4 know which promotions are driving engagement.

Where does it go? Add this event to any interaction that links through from a promotion.

dataLayer.push({
  event: 'select_promotion',
  ecommerce: {
    promotions: [{
      promotion_id: 'GA-Train-Apr-25',
      promotion_name: 'GA4 Training April 2025',
      creative_name: 'Banner 1',
      creative_slot: 'Homepage Banner'
    }]
  }
});

The begin_checkout Event

What is it? Marks the first step of the checkout process.

What does it do? Allows GA4 to track how many users start checkout versus drop off at earlier stages.

Where does it go? Place it on the first page or action that moves a user into checkout.

dataLayer.push({
  event: 'begin_checkout',
  ecommerce: {
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      price: 10.99,
      item_brand: 'Propellernet',
      item_category: 'Shorts',
      item_variant: 'Blue',
      quantity: 1
    }]
  }
});

Checkout Option Events

What are they? add_shipping_info and add_payment_info are sent when users choose a shipping tier or a payment method.

What do they do? Track options users select during checkout that affect delivery and payment preferences.

Where do they go? Fire add_shipping_info when a shipping method is selected, and add_payment_info when a payment method is chosen.

Shipping Info:

dataLayer.push({
  event: 'add_shipping_info',
  ecommerce: {
    shipping_tier: 'Express',
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      quantity: 1
    }]
  }
});

Payment Info:

dataLayer.push({
  event: 'add_payment_info',
  ecommerce: {
    payment_type: 'Credit Card',
    items: [{
      item_id: '345678',
      item_name: 'Product 1',
      quantity: 1
    }]
  }
});

The purchase event

What is it? Sent after a successful transaction.

What does it do? It finalises the ecommerce flow, sending total revenue, tax, coupon usage, shipping, and product details.

Where does it go? Fire this once, on the confirmation or order success page only.

dataLayer.push({
  event: 'purchase',
  ecommerce: {
    transaction_id: 'T123',
    affiliation: 'Online Store',
    value: 22.99,
    tax: 4.60,
    shipping: 2.00,
    currency: 'GBP',
    coupon: 'SUMMER_SALE',
    items: [
      {
        item_id: '345678',
        item_name: 'Product 1',
        price: 10.99,
        quantity: 1,
        item_brand: 'Propellernet',
        item_category: 'Shorts',
        item_variant: 'Blue'
      },
      {
        item_id: '32145',
        item_name: 'Product 2',
        price: 5.00,
        quantity: 2,
        item_brand: 'Propellernet',
        item_category: 'Shirt',
        item_variant: 'Red'
      }
    ]
  }
});

The refund Event

What is it? Sent when a transaction (or part of it) is refunded.

What does it do? Tracks loss of revenue and helps correct product revenue attribution.

Where does it go? Trigger this when an online refund is successfully issued. GA4 supports both full and partial refunds.

Full refund:

dataLayer.push({
  event: 'refund',
  ecommerce: {
    transaction_id: 'T123'
  }
});

Partial refund:

dataLayer.push({
  event: 'refund',
  ecommerce: {
    transaction_id: 'T123',
    items: [
      { item_id: '345678', quantity: 1 },
      { item_id: '32145', quantity: 1 }
    ]
  }
});

Need help implementing these Data Layers? Join our GA4 training or check out our Analytics services.

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