Convert scaled bytes to raw bytes

DiskManager.php

/**
     * Convert string such as '500mb' to bytes. Converts KB, MB, GB, TB, PB) The strings
     * are case insensitive (mb=MB=m=M, k=K=kb=KB=Kb=kB)
     * 
     * Usage:
     *      $bytes = convertToBytes("512kb");
     * 
     * @param string $from
     *
     * @return bool|integer
     */
    public function convertToBytes($from)
    {
        preg_match('/^(?<from>\d+)(?<scale>[a-zA-Z]+)$/', $from, $matches);

        if ( !isset($matches['from']) or !isset($matches['scale']) )
        {
            return false;
        }
        $from  = $matches['from'];
        $scale = $matches['scale'];

        // kilobytes
        if ( preg_match('/(kb|k)/i', $scale) )
        {
            return $from*1024;
        }
        elseif (preg_match('/mb|m/i', $scale) )
        {
            return $from*pow(1024,2);
        }
        elseif (preg_match('/gb|g/i', $scale) )
        {
            return $from*pow(1024,3);
        }
        elseif (preg_match('/tb|t/i', $scale) )
        {
            return $from*pow(1024,4);
        }
        elseif (preg_match('/pb|p/i', $scale) )
        {
            return $from*pow(1024,5);
        }
        else
        {
            return $from;
        }
    }