The thumbnail product images in the listing pages can be set to any of the predefined sizes, from the Settings - Catalog settings menu. The available sizes are 160x160 px, 190x190 px, 220x220 px, 250x250 px, 275x275 px.
If you wish to change the thumbnail size for all the product images, you must launch the thumbnail resize process, by checking the corresponding option in the Catalog Settings page.
The resizing process can be launched only once within 24 hours.
If you do not launch the image resizing process, your new settings will only apply to the images uploaded after changing the settings.
Important: Please note that changing the size of the thumbnail images may affect the way in which your listing pages are currently displayed.
Listed in: Catalog settings