How do I set the featured image size on the single post?

Question

Good day! I've tried searching for the answer from other posts, but overrides didn't seem to work for me. Basically every time I have a single post the featured image is the first image and it's always so much larger than the rest of the image. When I try to resize by editing, it only changes the resolution.

Additionally, on mobile it remains the same big size, while my other added media become optimised for mobile. Help anyone?

Answer 1

You can set the featured image size in second parameter based on this document

// without parameter -> Post Thumbnail (as set by theme using set_post_thumbnail_size())
get_the_post_thumbnail( $post_id );                   

get_the_post_thumbnail( $post_id, 'thumbnail' );      // Thumbnail (Note: different to Post Thumbnail)
get_the_post_thumbnail( $post_id, 'medium' );         // Medium resolution
get_the_post_thumbnail( $post_id, 'large' );          // Large resolution
get_the_post_thumbnail( $post_id, 'full' );           // Original resolution

get_the_post_thumbnail( $post_id, array( 100, 100) ); // Other resolutions

actually php cant check the responsive of screen. But if you want check the user run in mobile or not you can use this function.

if ( wp_is_mobile() ) {
    echo get_the_post_thumbnail( $post_id, 'large' ); 
} else {
    echo get_the_post_thumbnail( $post_id, 'thumbnail' ); 
}