FileSizeCalc

<?php
**
 * Parse file size
 *
 * @param  string $size    File size
 * @param  string $default Default size
 * @return string
 */
function ai1wm_parse_size( $size, $default = null ) {
	$suffixes = array(
		''  => 1,
		'k' => 1000,
		'm' => 1000000,
		'g' => 1000000000,
	);

	// Parse size format
	if ( preg_match( '/([0-9]+)\s*(k|m|g)?(b?(ytes?)?)/i', $size, $match ) ) {
		return $match[1] * $suffixes[ strtolower( $match[2] ) ];
	}

	return $default;
}