With wp_tag_cloud
you can set the smallest
and largest
argument to the same value:
$args = array(
'smallest' => 8,
'largest' => 8,
);
echo wp_tag_cloud($args);
Unfortunately, that would require hacking the Core. Also, unfortunately, I don't see a filter that will allow you to alter those argument directly, so you are going to have to do this a bit brute-force-y.
add_action(
'load-edit-tags.php',
function () {
add_filter(
'wp_generate_tag_cloud',
function ($return) {
$pat = '|font-size: [0-9]+([^;]+)|';
return preg_replace($pat,'8$1',$return);
},
1,2
);
}
);
Hooking to load-edit-tags.php
should cause this to operate only on the wp-admin/edit-tags.php
page on the backend, which is what I assume you want.
Reference: http://codex.wordpress.org/Function_Reference/wp_tag_cloud