Sakari offers a free web-based calculator to help you check the length of your message before sending it. Predictably, it's called the SMS Length Calculator, and you can find it here.
The calculator can:
- tell you how long your initial message is
- identify and highlight special (non-GSM-7) characters that will affect the message cost
- allow you to edit out unintended special characters, providing a 'clean' version to paste into Sakari