WordPress image sizes

To get a list of all the registered image sizes in a WordPress installation, use:

wp_get_registered_image_subsizes();

This returns something like this:

[
    "thumbnail" => [
        "width" => 150,
        "height" => 150,
        "crop" => true,
    ],
    "medium" => [
        "width" => 300,
        "height" => 300,
        "crop" => false,
    ],
    "medium_large" => [
        "width" => 768,
        "height" => 0,
        "crop" => false,
    ],
    "large" => [
        "width" => 1024,
        "height" => 1024,
        "crop" => false,
    ],
    "1536x1536" => [
        "width" => 1536,
        "height" => 1536,
        "crop" => false,
    ],
    "2048x2048" => [
        "width" => 2048,
        "height" => 2048,
        "crop" => false,
    ],
]