How to create thumbnails with a fixed width, so all of them will have the same width?

right now, a thumbnail will be either 150px in height or in width, depending if it’s landscape or portrait. Is there a way to make them always the same width and scale them in height accordingly, without squaring them?

Kind regards

Use add_image_size() in your functions.php:

add_image_size( 'post-icon', 150);

…and then use this in your template:

<?php the_post_thumbnail('post-icon'); ?>