Featured Image Pro plugin allow create custom image sizes for your site. Once you install and activate this plugin you can set custom image size for wordpress.The custom size only works for new images you upload to the media library. When you upload image after insert custom size it will make all image size as you defined in Wp-content/uploads folder.

Register New Custom Size Images

Step 1Go to Settings page from ‘Featured Image Pro’ plugin.
Step 2Set the width and height of your images in pixels.

Custom Image Size

Step 3Then Click Save Settings.

Video Tutorial