There is no limit to how long an iMessage can be, with SMS it looks a little different. The default limit is 140 characters.
You can attach a maximum of three SMS messages to each other, i.e. write 420 characters. However, when sending more than 140 characters, the receiving person may not receive the SMS.
This is usually due to the recipient's smartphone or the mobile phone provider used by the recipient. So it now makes sense to leave the characters at a maximum of 140 and then send the SMS.
However, it is important that you can track the number of characters you have entered. You can activate the option to count the number of written characters on the iPhone as follows: iPhone:
How to activate the character counter in the message application under iOS
1. Open Settings --> Messages.
2. Scroll down until you see the SMS/MMS area.
3. Set the "Number of characters" slider to active
This only applies to text messages on your iPhone!
Now you always know how many characters you write in an SMS.