Ad density
The point where another ad starts costing you money
Past the Coalition for Better Ads 30% line, one more unit does not add revenue. It subtracts it, and Chrome enforces part of the penalty directly.
By Mario Bailey · Published
Every publisher who watches RPM knows the temptation: revenue is a little soft this week, so add another unit. There is a ceiling where that stops working and starts reversing, and it is not a soft guideline. Cross the main line and Chrome can pull your ads for you.
The 30% line is a limit, not advice
The Coalition for Better Ads sets a hard standard for mobile: ads may not exceed 30% of the vertical height of the page's main content. Above that, you are running one of the experiences the standard classifies as disruptive, whether the ads are text, image, or video. This is not just etiquette, because Chrome's built-in ad filter is tied to the standard: a site that consistently violates it can have all of its ads removed in Chrome, which is the majority of most publishers' traffic. The downside of the last ad is not a lower RPM. It is zero ads for most of your readers.
Below that line, three quieter costs
Even before the Chrome cliff, past a point each new unit costs more than it adds:
- Viewability dilutes. Our own placement study found a 60-point viewability spread by position, and the units publishers pile on are the ones at the bottom of that chart, the page-bottom and in-feed slots most readers never reach. An impression that is not viewable barely pays.
- Core Web Vitals degrade. More ads mean more layout shift and more main-thread work, which hurts the CLS and INP scores that feed a Google ranking signal. Fewer visitors next month, then fewer impressions.
- Readers leave. A page that is harder to read than to close loses the session, and every downstream impression with it.
The net-positive test, applied to count
This is why we do not target an ad count. We ask of each unit whether it is net-positive: does it earn more than it costs in viewability, speed, and reader patience? Our fill-rate study found the site that filled fewer of its ad requests earned more than double the page RPM. Density behaves the same way. The winning layout is almost always fewer, better-placed units, not more of them.
How to find your own ceiling
- Measure your mobile ad-to-content ratio against the 30% line first. That is the one with a Chrome penalty attached, so it is the floor you never cross.
- Then cut, do not add. Pull the lowest-viewability units, your placement data will name them, and watch whether RPM holds. It usually does, because those units were not earning.
- Treat any new unit as guilty until it proves net-positive on viewability and Core Web Vitals, not merely present on the page.