Initial + Sub Load
Set file size limits for initial load and subload phases to ensure ads don't slow down pages.
Are heavy ads slowing down your pages?
Ads that load too many assets during page load compete with content for bandwidth, slowing down the entire page. This hurts user experience and viewability, and if your ad hasn't rendered by the time visitors scroll past, you've lost the impression.
What are initial load and subload?
The IAB divides ad loading into two phases, separated by the browser's load event. Initial load includes all files requested while the page is loading, before the page has finished rendering. Subload includes all files requested after the page has finished loading.
Well-behaved ads keep initial load lightweight so they don't compete with page content, then load heavier assets during subload when bandwidth is available.
What this test measures
Advalidation measures the total file size of assets loaded during each phase. You can set limits for initial load, subload, or both to ensure creatives meet your performance requirements.
How to evaluate your results
Set your ad specification limits based on your requirements or IAB guidelines.
- Initial Load limit - Typically 150-300 KB for standard display ads
- Subload limit - Typically 300-500 KB for additional assets
- Combined limit - Some specs set a total limit for both phases