I've this line: <?php the_post_thumbnail( array(140,180) ); ?> However it still does not display the best dimensions, it is possible to method to achive the precise dimensions which i want?

Try adding a custom image size first and taking advantage of a mention of the that definition: http://codex.wordpress.org/Function_Reference/add_image_size

In functions.php

if ( function_exists( 'add_theme_support' ) ) {
    add_theme_support( 'post-thumbnails' );
    set_post_thumbnail_size( 150, 150 ); // default Post Thumbnail dimensions   
}

You'll be able to use <?php the_post_thumbnail( 'post-thumbnails' ); ?>