E-commerce tracking in GA4: how to measure your webshop

GA4 doesn't measure e-commerce by itself: your webshop has to pass on every step as an event ^[1]. At a minimum, measure purchase, with a unique transaction ID, an items list, a value as a number and the currency. Send refunds with refund, add payment pages to your unwanted referrals and compare your GA4 revenue with your webshop's every month.

Whether you set it up yourself, ask your web developer or bring in a Google Analytics agency: the choices are the same. The most important one is what you put in value, because GA4, Google Ads and your own reporting must use the same number.

Which events do you need?

Start with purchase, then add the steps leading up to it. Use the names Google recommends: GA4 automatically fills reports with them, such as Ecommerce purchases ^[1].

With the first four you see where visitors drop off. Google has more, including events for product lists, shipping and payment information and internal promotions ^[2]. If you use Shopify, the Shopify pixel measures some events automatically: check which ones, so they don't fire twice alongside your own tags ^[1].

Which parameters belong to a purchase?

For purchase, two parameters are required, and the rest determines whether your revenue figures are usable ^[2].

A number means without a currency sign: 72.05, not "€ 72,05" ^[4]. Optional parameters include coupon and customer_type (new or returning), for which Google recommends a 540-day window ^[2].

What do you put in value?

Google recommends value excluding shipping and tax; you send those separately in shipping and tax ^[2]. For a Belgian webshop that shows prices including VAT, that is a deliberate choice.

Both can work, as long as you use one definition. If you switch from month to month, or Google Ads uses a different value than GA4, your bid strategy steers on a different number from the one you report on.

How to send a purchase

With Google Tag Manager, your webshop pushes the data to the data layer, and a GA4 tag passes it on. Clear the previous ecommerce object first, so data from an earlier step doesn't carry over ^[5]:

dataLayer.push({ ecommerce: null });
dataLayer.push({
  event: 'purchase',
  ecommerce: {
    transaction_id: 'BE-10482',
    value: 59.50,
    tax: 12.50,
    shipping: 4.95,
    currency: 'EUR',
    items: [{
      item_id: 'SKU-231',
      item_name: 'Tuinhandschoenen leder',
      price: 29.75,
      quantity: 2
    }]
  }
});

Here the prices exclude VAT: value is 2 x 29.75 = €59.50. In the GA4 event tag, tick Send Ecommerce data under More Settings › Ecommerce, and a Custom Event trigger on purchase fires the tag ^[5].

Ask your web developer or platform to make sure the events follow Google's names exactly, and that purchase only fires once the order has been placed, not on the click on "Place order". Test every change in DebugView: in the standard reports, e-commerce data can take up to 24 hours to appear ^[1].

Duplicate purchases and refunds

The transaction ID protects you against duplicate purchases, for example when a customer reloads the confirmation page: GA4 deduplicates purchases with the same ID, but only for web streams ^[3]. Never send an empty or fixed ID, because GA4 will then filter out real orders ^[3]. How to track down duplicate or unknown transactions is covered in Fixing (not set), spam and duplicate purchases in GA4.

You report a refund with refund, with the same transaction ID and the refunded items in the items list ^{[1], [5]}. Purchase revenue deducts refunds, Gross purchase revenue does not ^[6]. Because a refund usually happens in the back office, ask your web developer explicitly how the refund event is sent.

Payment pages as unwanted referrals

If a customer pays on the page of a payment provider or their bank, GA4 can see their return as a new visit from that domain. The payment provider then gets the sale, not the campaign that brought the customer; Google uses this example itself ^[7]. Add those domains to the unwanted referrals in your web stream's tag settings, up to 50 per stream ^[7].

You can see which domains they are in your Traffic acquisition report. To find them, test a payment with every payment method you offer.

Checking revenue and sending it to Google Ads

GA4 and your webshop never show exactly the same figure. The question is whether the difference is explainable and stable.

A difference that stays the same size month after month is usually consent. A sudden jump after an update to your webshop, theme or banner points to an error.

To steer campaigns on revenue, turn purchase into a conversion in Google Ads; conversions from GA4 are set to secondary by default ^[9]. How to make that choice is explained in GA4 key events and conversions: the difference explained. For Shopping campaigns that value has to be right: see How to set up a Google Shopping campaign: step by step for online stores.

Not sure whether your e-commerce measurement adds up? The free tracking audit checks which events fire, which parameters they send and whether purchases count once.