gavargas

I found out how through the

<?php wp_get_attachment_image_src( $attachment_id, $size, $icon ); ?>

This is what I did:

<?php
$cardimgdata = wp_get_attachment_image_src( get_post_thumbnail_id(), 'single-thumb' );
$imgwidth = $cardimgdata[1];
?>

Then I echo the value of the width [1]:

<?php echo $imgwidth ?>

single-thumb is the name of the thumbnail size I declared in the functions.php file you can substitute it for whatever you have on your functions.php file.

For more information here is where I obtained the code from:

http://codex.wordpress.org/Function_Reference/wp_get_attachment_image_src