Reply To: Featured Image Default Size on Single Post

[Tom]

This post should help then: https://generatepress.com/forums/topic/featured-image-default-size-on-single-post/#post-233803

If you don’t use one of the WP generated sizes (full, medium, thumb), you can create your own:

add_action('after_setup_theme', 'tu_add_image_sizes');
function tu_add_image_sizes()
{
    add_image_size( 'custom-image-size1', 300, 9999 ); //300 pixels wide (and unlimited height)
    add_image_size( 'custom-image-size2', 220, 180, true ); //(cropped)
}