Changing thumbnail sizes in WordPress is remarkably easy. click on WP dashboard navigate to the settings media click look for image sizes thumbnail size change. the default width and height of your thumbnails in pixels and that is pretty much it. but, let’s dive a little bit deeper as you can see the default thumbnail size is a square image this employs a hard crop since. we enable the setting crop thumbnail to exact dimensions. what this means is? that WordPress will take the film. they’ll size you set fill the area with the image. we use and leave the rest of the image a soft crop on the next hand is a resize that shrinks your images. while retaining their proportions once you set a new default thumbnail size. WordPress will use it for all images. you upload from that moment on however what if you already have a sizeable media library that uses other thumbnail sizes instead of reuploading those images. you can simply resize them the best tool for that job is the Ajax thumbnail rebuild plug-in what this plug-in does is takes all of your existing thumbnails and resizes them one by one. it also works on the other image sizes that WordPress uses such as medium large and so on to get started install and activate the plug-in. first you do go to the settings rebuild topic tab and choose the images. you want to resize and then click the rebuild all thumbnails button add new default image sizes to WordPress. you’ll need to edit your themes function step PHP file connect via FTP navigate to wp-content slash themes’ and open the functions dot PHP file add this snippet of code at the bottom. this code by the way will be available in the blog. here code explains how it works east well once it tells WordPress that you want to add new image sizes in your theme. then, it creates a new default option and registers it the 660 is the width in the 480 is the height feel free to add any custom sizes. you are using a letest line for each save the changes to your functions that PHP file and the new options should appear in your WordPress editor and there we go now you know how to change thumbnail sizes in WordPress.