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Every SMS message is split into one or more segments before delivery. The number of segments determines your per-message cost — Trackly bills per segment, not per message.

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What is a Segment?

A segment is a fixed-size chunk of an SMS message. Short messages fit in one segment. Longer messages are split across multiple segments, each with overhead bytes for reassembly headers.

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GSM-7 vs UCS-2 Encoding

SMS supports two character encodings. The encoding is chosen automatically based on the characters in your message.
EncodingCharacter SetSingle SegmentMulti-Segment (per part)
GSM-7Latin letters, digits, common symbols160 characters153 characters
UCS-2Full Unicode (emoji, non-Latin scripts)70 characters67 characters
If every character in your message is in the GSM-7 basic set, the message uses GSM-7 encoding. If any character falls outside GSM-7, the entire message switches to UCS-2.

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GSM-7 Basic Character Set

The GSM-7 basic set includes:
  • Letters: A-Z, a-z
  • Digits: 0-9
  • Symbols: @ £ $ ¥ ! " # ¤ % & ' ( ) * + , - . / : ; < = > ? ¡ ¿ § _
  • Accented characters: è é ù ì ò Ç Å å Ä ä Ö ö Ñ ñ Ü ü à Æ æ ß É
  • Greek letters: Δ Φ Γ Λ Ω Π Ψ Σ Θ Ξ
  • Special: Ø ø and standard whitespace (space, newline, carriage return)

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Characters That Trigger UCS-2

These commonly used characters force UCS-2 encoding, dramatically reducing your per-segment character limit:
  • Emoji (any emoji forces UCS-2)
  • Smart quotes: \u201c \u201d \u2018 \u2019 (use straight quotes ” ’ instead)
  • Em dash: \u2014 (use a hyphen - instead)
  • Ellipsis character: \u2026 (use three periods … instead)
  • Non-Latin scripts: Chinese, Arabic, Cyrillic, etc.
A single emoji in a 160-character message increases it from 1 segment (GSM-7) to 3 segments (UCS-2), tripling the cost.

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Segment Calculation

The platform calculates segments using this algorithm:
  1. Check if all characters are in the GSM-7 basic character set
  2. If GSM-7: use 160-char limit (single) or 153-char limit (multi-part)
  3. If UCS-2: use 70-char limit (single) or 67-char limit (multi-part)
  4. Divide the message length by the per-segment limit, rounding up

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Examples

MessageLengthEncodingSegments
”Your order ships today.”24 charsGSM-71
”Your code is 482910. Valid for 5 min.”38 charsGSM-71
”Big sale! Save 50% on all items. Shop now at…“160 charsGSM-71
”Big sale! Save 50% on all items. Shop now at…“161 charsGSM-72 (153 + 8)
“Thanks for signing up! \ud83c\udf89”25 charsUCS-21
A 140-character message with one emoji140 charsUCS-22 (70 + 70)

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Billing Impact

Trackly bills per segment at tiered rates:
  • First 1M segments (in a 360-day cycle): $0.0045/segment
  • After 1M segments: $0.0030/segment
A 2-segment message costs twice as much as a 1-segment message. Keeping messages within the single-segment GSM-7 limit (160 characters) is the most cost-effective approach.

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Tips for Reducing Segments

  1. Avoid emoji — they force UCS-2 encoding and cut your limit from 160 to 70 characters
  2. Use straight quotes — replace smart quotes (\u201c \u201d) with straight quotes (” ”)
  3. Use short links — Trackly’s link shortener creates compact URLs that save characters
  4. Keep messages under 160 characters — one GSM-7 segment is the sweet spot for cost and deliverability
  5. Test with the API — send a test message and check the segments field in the response

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Template Length Cap

Creative templates are limited to 1,600 characters. This prevents accidentally creating messages that would produce an excessive number of segments.

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Next Steps

Creative Templates

Design effective message templates

Platform Limits

View all platform limits