One text message is 160 characters.
Sometimes we know that you will need more than those 160 characters to keep your customers updated. This is when you can use a concatenated SMS, which means to use multiple text messages to make up one long message. Textburst will allow you to send up to 459 characters which is effectively three text messages.
Once you've inputted your contacts, the SMS counter below the 'Your message' field will update you on the number of messages you'll be sending.