How To Change Default Image Thumbnail Sizes in Wordpress

I answered my own question folks, and I feel quite dumb.. haha.

It was in the Admin screen. Left bar.. Settings -> Media, and there they are. Thumbnail, medium, and large sizes. No file hacks, no custom size settings in the functions.php file necessary.

Oops!

In function.php add this code:

update_option( 'thumbnail_size_w', 250 );update_option( 'thumbnail_size_h', 141 );update_option( 'medium_size_w', 850 );update_option( 'medium_size_h', 478 );update_option( 'large_size_w', 1200 );update_option( 'large_size_h', 675 );

Image Size Names : ‘thumb’, ‘thumbnail’, ‘medium’, ‘large’

The names “thumb” and “thumbnail” are just aliases

Look in your wordpress root folder as such:

wordpress_root\wp-includes

In this folder there is a file called: media.php

Starting on Line 34 there is a function:

function image_constrain_size_for_editor($width, $height, $size = 'medium')

in this function, starting on Line 41, there is the following code. Just edit this for your needs:

elseif ( $size == 'thumb' || $size == 'thumbnail' ) {        $max_width = intval(get_option('thumbnail_size_w'));        $max_height = intval(get_option('thumbnail_size_h'));        // last chance thumbnail size defaults        if ( !$max_width && !$max_height ) {            $max_width = 128;            $max_height = 96;        }    }