SMS Segment & Character Calculator
Calculate exact SMPP message segments, byte limits, and character encodings to avoid split SMS charges in real time.
GSM-7 vs UCS-2 Encoding Mechanics
Standard SMS networks use GSM 03.38 7-bit default alphabet, which packs 160 characters into a single 140-byte (1,120-bit) signaling packet.
The presence of even a single non-GSM character (such as Cyrillic, emoji, accented glyphs, or curved quotes) forces carriers to switch the entire message to UCS-2 16-bit encoding, dropping the single-message limit from 160 to 70 characters instantly.
Why Concatenated Messages Reduce Segment Limits
When an SMS exceeds the single segment threshold, carriers split the message into multipart packets. To allow recipient devices to reassemble the message correctly, each segment carries a 6-byte User Data Header (UDH).
- GSM-7 multipart: 153 characters per segment (7 characters reserved for UDH).
- UCS-2 multipart: 67 characters per segment (3 characters / 6 bytes reserved for UDH).
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Diagnose 10DLC carrier filtering, shortcode blocks, and delivery latencies.
curl -X POST https://smsriver.com/api/v1/tools/segment-calc/ \
-H "Content-Type: application/json" \
-d '{"text": "Your SMSRiver verification token is: 849-204"}'