Google Attribution will allow advertisers to see whether online ad campaigns generate offline sales.
Announcing the service, Google said that it captures around 70% of credit and debit card transactions in the US.
Critics said it represented another blow to privacy.
Google announced the new product in a blogpost, saying: "For the first time, Google Attribution makes it possible for every marketer to measure the impact of their marketing across devices and cross-channel - all in one place."
