This is the default WordPress Gallery that comes standard with every installation of WordPress and is not dependent on our theme. The size of the thumbnails is set in WordPress Media settings and is not controlled by the theme.

There is no limit to the number of images or image galleries that you can make with WordPress. The image thumbs can also be larger or smaller.

This is the default WordPress Gallery that comes standard with every installation of WordPress and is not dependent on our theme. The size of the thumbnails is set in WordPress Media settings and is not controlled by the theme. For different size thumbnails recreate them using the Regenerate Thumbnails plugin.

There are 2 plugins that you could use instead of the above.
NextGen Gallery and FooGallery. Both have options that you can easily apply.