sizeFormat function for PHP - Extracted from WordPress core

sizeFormat.php

<?php

/**
 * Convert number of bytes largest unit bytes will fit into.
 * Extracted from WordPress core to work as a standalone function.
 *
 * @link https://codex.wordpress.org/Function_Reference/size_format
 *
 * @param int|string $bytes    Number of bytes. Note max integer size for integers.
 * @param int        $decimals Optional. Precision of number of decimal places. Default 0.
 *
 * @return string|false False on failure. Number string on success.
 */
function sizeFormat( $bytes, $decimals = 0 ) {
	$quant = array(
		'TB' => 1e+12,
		'GB' => 1073741824,
		'MB' => 1048576,
		'kB' => 1024,
		'B'  => 1,
	);

	foreach ( $quant as $unit => $mag ) {
		if ( doubleval( $bytes ) >= $mag ) {
			return number_format( $bytes / $mag, $decimals ) . ' ' . $unit;
		}
	}

	return false;
}