How to modify default size of thumbnails

Two possible ways, either works.

1. Use a plugin:
https://www.shiftthis.net/wordpress-thumbnail-size-plugin/

2. Add code to your theme’s functions.php file:

function custom_thumbnail_size() {
return 128; // or whatever number of pixels you want
}
add_filter('wp_thumbnail_max_side_length','custom_thumbnail_size');

ok, now is working rigth. Thanks a lot!

This was helpful. How can I also set the thumbnail’s height? I need the thumbnail to be square. Thanks

How do I modify default thumbnail height so image will be square? This code that I’m using only sets the width. Thanks

well i think for that you need a plugin because normally wordpress only works with a max size on any side not a fixed thumbnail size.