One of the best features of the updated Jetpack by WordPress.com plugin is the Tiled Galleries where you can create elegant magazine-style mosaic layouts for your photos without having to use an external graphic editor. This is very cool and you can create galleries that look like what you see below.
One issue that I, and other users have run into is the width of the gallery not filling the width of the content area that it sites in when the page is drawn. And looking at the DOM elements in the page we see that the widths are all inline CSS, so we know that this is doing something on the fly, right?
Well, it turns out that images used in tiled galleries require extra-special processing, so they are served from WordPress.com’s CDN, even when the Photon (WordPress.com content delivery network) module is disabled.
The tiled/square/circle galleries use the
$content_width setting of your theme (if you are lucky to have it set); otherwise, it defaults to 500-px wide. In your theme’s functions.php file, try adding this:
if ( ! isset( $content_width ) ) $content_width = 750;
Replace the 750 with the width that you need for the full width of your content to be reached. If that fixes the problem, consider contacting the theme author to have them add
$content_width to their themes more permanently.