A cross-device conversion is a conversion that happens on a different device from the one where the person interacted with your ad. Someone taps your ad on their phone on the train, then books on their laptop at home that evening: Google Ads can credit that booking to the phone click.
How cross-device conversions work
A standard website conversion is matched to the ad click through a click identifier stored in a first-party cookie on the device that clicked. When the person converts on another device, that cookie is not there, so the connection has to be made another way.
Google does this mainly through people who are signed in to a Google account on both devices, for example through Chrome, Android or YouTube, and through modelling that estimates the rest from patterns in that signed-in data. Enhanced conversions add another route by matching hashed customer details, such as the email address entered at checkout, to signed-in Google accounts, where consent allows.
Cross-device conversions are included in the Conversions column by default. You can see them separately by adding the Cross-device conv. column, and the attribution reports can show journeys that move between devices. At the time of writing (October 2026), these are part of standard reporting, though column names do change from time to time.
Why it matters
Plenty of UK purchase journeys start on a phone and finish on a computer, especially for considered buys such as furniture, holidays, legal services or business software, where people research on the move and act at a desk. Without cross-device measurement, mobile campaigns look as if they produce clicks and nothing else, and it is tempting to cut mobile budgets that are in fact starting sales.
It also explains why Google Ads and GA4 often disagree. Google Ads credits the click across devices where it can; GA4 may record the same sale as a direct or organic visit on the laptop, depending on settings such as Google Signals and on consent. Neither is necessarily wrong. They measure different things in different ways.
Common mistakes
- Judging device performance on the device where people converted, rather than the device where they clicked the ad.
- Treating cross-device numbers as exact counts. Part of them is modelled, so read them as a well-informed estimate.
- Expecting full cross-device credit when many visitors decline cookies. Under UK GDPR and PECR, people who refuse advertising cookies limit what can be matched; consent mode fills some of the gap with modelling.
- Skipping enhanced conversions on a lead form or checkout, which leaves straightforward matches unmade.
- Cutting a mobile campaign on last-device data from GA4 alone, without checking what Google Ads reports for the same period.
How to act on it
Add the Cross-device conv. column to your campaign and device reports and see how much of each campaign’s total it accounts for. A large share on mobile-heavy campaigns suggests phone clicks are starting journeys that finish elsewhere, which should shape bid and budget decisions.
Make sure enhanced conversions are switched on and working for your forms or checkout, and that your cookie banner passes the right consent signals to Google’s tags. If you keep a CRM, record the source campaign of each lead so you can compare it with what Google reports. Checking this measurement is part of the account audit in my PPC management service.