For an ad entering an auction on the Display Network, the Google Ads system will calculate the effective cost–per–thousand impressions (eCPM) when there are:

• any cost–per–click (CPC) or cost–per–acquisition (CPA) ads entering the auction
• only cost–per–click (CPC) ads entering the auction
• only viewable cost–per–thousand impressions (vCPM) ads entering the auction
• both cost–per–click (CPC) and cost–per–acquisition (CPA) ads entering the auction