SMS segments and character limits

💡 Tip: Avela shows a live character count as you compose an SMS. If the counter turns red and displays "SMS message exceeds character limit" when trying to send it, your message has exceeded the two-segment maximum and must be shortened before it can be sent.

Why just two segments? 

Each segment sent counts as one SMS message for billing purposes. This means a two-segment message costs twice as much to deliver as a single-segment message — multiplied across every recipient in your send. For large sends (such as the ad-hoc messaging shown above, with 254 recipients), the difference between one and two segments doubles the SMS cost for that send. For automatic messages triggered by form activity, costs accumulate over time as families complete forms throughout an enrollment period.

To help manage costs, Avela limits messages to two segments maximum. Messages that would require three or more segments cannot be sent and must be shortened.

How language affects segmentation

When you send messages to families in multiple languages, or use Avela's Translate to multiple languages feature, each language version of your message is evaluated independently for encoding and segment count.

Things to watch out for:

• Spanish, French, and other Latin-script languages typically remain within GSM-7 encoding, though characters like é, ñ, ç, or ü are part of the GSM-7 extended character set and count toward the limit. Always check the character count after translation.
• Languages using non-Latin scripts (e.g. Arabic, Chinese, Korean) will always trigger UCS-2 encoding, significantly reducing the available character count.
• Bilingual messages — where both English and a second language are included in the same SMS — are common in Avela. If the combined text exceeds the two-segment limit, or if the second language introduces UCS-2 characters, you will need to shorten the message.

When composing a bilingual SMS, aim to keep your total character count under 306 characters if the message uses only standard Latin characters, or under 134 characters if any non-GSM characters are present. 

Tips for staying within limits

• Draft in plain text and avoid punctuation like curly quotes (" "), em dashes (—), or ellipsis characters (…) — these are UCS-2 characters and will reduce your limit dramatically. Use straight quotes ("), hyphens (-), and three periods (...) instead.
• Use the live character counter in the SMS content field. The counter displays your current count against the segment limit (e.g. 131/153 for a single GSM-7 segment).
• Translate carefully. After using the Translate to multiple languages feature, review the character count for each language version before sending.
• Keep bilingual messages concise. Since both languages must fit within the same two-segment limit, be more concise than you might be for email.

For more on Twilio's SMS character encoding standards, see the Twilio SMS character limit guide.