WooCommerce 3.3 Image Size Changes
WooCommerce 3.3
got some Image Size Improvements. You can read all about that here.
This has caused a little confusion because if a theme defines the image sizes then a few options disappear.
What once looked like this:

Now looks like this:

The change is that these two settings have been hidden.
Main image
width andThumbnail width

If you see these missing, this is because you are on WooCommerce 3.3+
and the theme you are using has defined these sizes already.
This is really great in that a Theme Developer can define the size of images that are best optimized for the theme they are creating. But if you are familiar with these settings and they seem to disappear, it can be a little frustrating.
You can still override these values and set your own values if you would like. Just use the following filter.
add_theme_support( 'woocommerce', array(
'thumbnail_image_width' => 150,
'single_image_width' => 322,
) );
Add that snippet to your theme’s functions.php
file and change the values as you see fit.
I hope this helps. Thanks again for using WordPress and WooCommerce! (pssst … have you tried Jetpack yet? It’s awesome.)
Update 3.14.18
This is a really great article on this. Better than this one for sure. 🙂