WordPress at a glance
function is not described

get_space_used() WP 3.5.0

Returns the space used by the current blog.

Hooks in function
Return

Int. Used space in megabytes

Usage

get_space_used();

Code of get space used: wp-includes/ms-functions.php WP 5.2.2

<?php
function get_space_used() {
	/**
	 * Filters the amount of storage space used by the current site.
	 *
	 * @since 3.5.0
	 *
	 * @param int|bool $space_used The amount of used space, in megabytes. Default false.
	 */
	$space_used = apply_filters( 'pre_get_space_used', false );
	if ( false === $space_used ) {
		$upload_dir = wp_upload_dir();
		$space_used = get_dirsize( $upload_dir['basedir'] ) / MB_IN_BYTES;
	}

	return $space_used;
}