Output the width & height of an image using a particular image style In Drupal, you can use the following in a field--field-image.tpl.php file to output an image as a URL using a particular image style:

&lt;?php foreach ($items as $delta =&gt; $item): ?&gt;
&lt;?php echo image_style_url('thumbnail', $item['#item']['filename'] ); ?&gt;    
&lt;?php endforeach; ?&gt;


This will output all images as a URL with the Thumbnail style. 

I would like to get the width and height values of that image (with the thumbnail style). How can I do it?

I would like to do it without having to install any extra modules.
image_get_info() is the function that will get you the details. But it accepts uri as the param (Not sure about url). You can try passing the argument.
If you manage to get the path of the images then this function return the following ,


"width": Width, in pixels.
"height": Height, in pixels.
"extension": Commonly used file extension for the image.
"mime_type": MIME type ('image/jpeg', 'image/gif', 'image/png').
"file_size": File size in bytes.