The standard length of a text message is 160 characters. However, when you use special characters (i.e. Arabic, Greek, Russian), the amount of characters per SMS decreases. Remember that if you want to send SMS in special characters, you need to use unicode. In some countries, mandatory text or numbers take up extra characters, therefore the amount of characters that you can actually use is less. Check out specific country restrictions.
If you need to send a longer SMS, you can activate the 'Enable concatenated SMS' setting when you create a new integration.