Change post thumbnail size
To change post thumbnail size, First check your theme support function add_theme_support(‘post-thumbnails’);
Default WordPress Thumbnail
the_post_thumbnail( ‘thumbnail’ ); // Thumbnail (150 x 150 hard cropped)
the_post_thumbnail( ‘medium’ ); // Medium resolution (300 x 300 max height 300px)
the_post_thumbnail( ‘medium_large’ ); // Medium Large (added in WP 4.4) resolution (768 x 0 infinite height)
the_post_thumbnail( ‘large’ ); // Large resolution (1024 x 1024 max height 1024px)
the_post_thumbnail( ‘full’ ); // Full resolution (original size uploaded)
How do I force the WordPress post thumbnail to display at a fixed size?