With a lower conversion rate, assuming identical order value, the earnings per click will be lower on mobile than desktop. So with a $100 AOV and 5% CVR, your EPC is $5 per click.
With mobile, the CVR will be lower (at least from my experience), so your EPC may be $2.50 per click with a 2.5% CVR.
If you're converting worse, you just pay less per click. So if you want your ad expense to be 10%, with desktop ads, you can pay $.50 per click, versus only $.25 for mobile. Google's inventory growth has only come from mobile, which converts worse, so it is essentially less valuable. Google has mitigated this by increasing AdWords CTR, which increases their earnings per mille. YoY I've seen AdWords CTR increase ~30% on mobile, likely due to the green ad labels and increased spacing between ads that push organic results further down the page.
Google is pushing hard to get advertisers to actually bid more on mobile, even though it converts worse, by eliminating metrics such as Cost per Converted Click in favor of Cost/Conversion (which attributes conversions across devices. Until recently, Desktops & Tablets were lumped into one bidding category, the latter being the worst performing of all 3 devices, the former the best) and pushing equally opaque metrics such as Store Visits. The Store Visits functionality is touted as a huge way to measure cross device in person conversions that big brands with huge, inefficient budgets love (clicks desktop ad, visits store and store visit is logged by phone), but having worked at an out of the way retailer who would be closed on major US holidays, Store Visits held steady even though stores were closed. There isn't anything you can really do, though, since over 90% of all US search traffic is Google.
Yeah, the decoupling of desktop and tablet is a big deal for us, our tablet conversion rate is currently pretty similar to mobile but we have had to pay roughly double per click over mobile to have the bids correct for desktop.
With mobile, the CVR will be lower (at least from my experience), so your EPC may be $2.50 per click with a 2.5% CVR.
If you're converting worse, you just pay less per click. So if you want your ad expense to be 10%, with desktop ads, you can pay $.50 per click, versus only $.25 for mobile. Google's inventory growth has only come from mobile, which converts worse, so it is essentially less valuable. Google has mitigated this by increasing AdWords CTR, which increases their earnings per mille. YoY I've seen AdWords CTR increase ~30% on mobile, likely due to the green ad labels and increased spacing between ads that push organic results further down the page.
Google is pushing hard to get advertisers to actually bid more on mobile, even though it converts worse, by eliminating metrics such as Cost per Converted Click in favor of Cost/Conversion (which attributes conversions across devices. Until recently, Desktops & Tablets were lumped into one bidding category, the latter being the worst performing of all 3 devices, the former the best) and pushing equally opaque metrics such as Store Visits. The Store Visits functionality is touted as a huge way to measure cross device in person conversions that big brands with huge, inefficient budgets love (clicks desktop ad, visits store and store visit is logged by phone), but having worked at an out of the way retailer who would be closed on major US holidays, Store Visits held steady even though stores were closed. There isn't anything you can really do, though, since over 90% of all US search traffic is Google.