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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →SMS character counts change because different counters measure different things. One counts the characters you typed, another counts the encoding units a network carries, and a third reports how many separate messages the text will become. For a single SMS, the common ceilings are 160 GSM-7 units or 70 UCS-2 characters. Once a message is split into parts, each part carries less: 153 GSM-7 units or 67 UCS-2 characters. These are standards-based values, not guarantees for every carrier, provider or app, and the sections below explain where the differences come from.
The limits behind the count
Two encodings cover nearly every ordinary text message. GSM-7 uses the GSM alphabet and its extension table. UCS-2 carries text as 16-bit Unicode code units. The values below are the ones the cited standards and vendor documentation give for each.
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| Encoding | Single-message maximum | Per segment, multipart message | What counts as one unit |
|---|---|---|---|
| GSM-7 | 160 units | 153 units | A basic-alphabet character is 1 unit. An extension-table character such as ^ is 2 units. |
| UCS-2 | 70 characters | 67 characters | Each character is one 16-bit code unit. A non-GSM character can move the whole message into this encoding. |
Route-specific values can differ from these general figures. Twilio documents a separate multipart capacity for toll-free numbers sent to the US or Canada:
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| Route | GSM-7 per multipart segment | UCS-2 per multipart segment | Source |
|---|---|---|---|
| General multipart values | 153 | 67 | ETSI TS 100 901 (3GPP TS 03.40) |
| Toll-free numbers, US or Canada | 152 | 66 | Twilio SMS character-limit documentation |
Twilio presents the toll-free values as its own documented exception. The cited sources do not explain the header form behind the one-unit difference, so read them as Twilio’s figures rather than a rule for every toll-free number.
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Where the 140-byte payload and the header come from
SMS was built around a 140-byte user-data payload, a figure that Microsoft’s Azure Communication Services SMS FAQ also gives. That is 1,120 bits, and it explains both headline numbers: 160 GSM-7 units at 7 bits each (160 × 7 = 1,120) and 70 UCS-2 characters at 16 bits each (70 × 16 = 1,120).
A message longer than one segment carries a User Data Header so the receiving device can reassemble it. Twilio’s documentation says: The recipient’s device re-assembles the segments into the original message.
The header uses part of every segment’s payload. In the common header form described in the ETSI/3GPP specification, the header is six octets (48 bits). In GSM-7 it rounds up to seven septets, leaving 160 − 7 = 153 units. In UCS-2 it occupies three 16-bit characters, leaving 70 − 3 = 67. A different header form or route changes these figures, which is why the multipart numbers are not identical everywhere.
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Why the same text gets different counts
Most mismatches come from one of the five mechanisms below. Each is a different definition of what is being counted.
The counter may report different things
Android’s SmsMessage.calculateLength reference lists several outputs: the SMS count, the code units used, the units remaining before the next message, the encoding size, and language-table indicators. A simple counter may show only one of these. A count of 150 “characters” and a count of “1 message” can both be correct for the same text, because they answer different questions.
Extension-table characters cost two units
The GSM-7 extension table places characters such as ^, the curly and square brackets, the tilde, the vertical bar and the euro sign behind an escape code, so each uses two septets. Vonage’s concatenation guide uses This ^ That as an example: it has 11 typed characters but consumes 12 GSM-7 units. The Vonage guide covers the GSM character tables and this behaviour.
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One non-GSM character can switch the whole message to UCS-2
Twilio notes that a curly quote can force UCS-2. Emoji fall outside the GSM alphabet, so they produce the same switch. Once a message moves to UCS-2, the single-message ceiling drops from 160 units to 70 characters, and each multipart segment drops from 153 to 67. The switch applies to the whole message, not only the offending character.
Some services change this behaviour. Twilio describes Smart Encoding, which can replace certain non-GSM characters with equivalents, so the text recipients receive may not match what was typed. Vonage’s Messages API has a type=unicode setting that applies UCS-2 even to characters GSM-7 could represent. Check which of these is active before comparing counts across tools.
Crossing one segment boundary adds a header-sized cost
Twilio’s example shows the arithmetic. A 161-unit GSM-7 message is sent as two segments: 153 units in the first and 8 in the second. A message of exactly 160 units is one segment, so a single extra unit doubles the number of messages sent. This is why a message that looks only slightly longer can be billed or counted as much more.
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The route and number type change the limit
Beyond the toll-free exception above, Microsoft’s SMS FAQ warns that some wireless carriers or devices might act differently when they receive long messages.
The same FAQ describes a US short-code caveat for non-ASCII content beyond four segments. That caveat is specific to Azure Communication Services and should not be generalised to every sending route or carrier.
SMS and RCS are different delivery paths
Google’s RCS chats FAQ says RCS depends on carrier, region and device, and that Google Messages can send as SMS or MMS when RCS is unavailable. An SMS counter describes only the SMS path. When a conversation runs over RCS, the SMS count is an estimate of what would be sent, not a record of what was delivered.
iPhone and Android: what the evidence does and does not show
A common question is whether the limit differs between iPhone and Android. The vendor documentation cited here establishes the SMS figures above and shows that Android’s API exposes its own counting outputs. It does not include a current, controlled comparison of how Apple Messages and Android count identical text, so this article does not claim a fixed difference between them. If two phones show different numbers, check the channel (SMS or RCS), the encoding trigger and the sending route first. Those explain the differences documented above.
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What a multi-platform previewer should display
No cited vendor document describes a specific previewer, so this checklist is a design recommendation drawn from the variation above rather than a documented feature. A previewer that gives one number without context will mislead users whenever the channel, encoding or route differs. It should show:
- Channel: SMS, RCS, or unspecified.
- Encoding: GSM-7 or UCS-2, with the character that triggered any switch named.
- Unit: characters, GSM-7 units or code units, labelled explicitly.
- Segments: the segment count and the units remaining before the next segment.
- Route assumptions: provider, number type (standard, toll-free or short code) and country.
- Encoding policy: whether unicode forcing or Smart Encoding is active.
- Confidence label: an explicit estimate marker when route data is missing, with no promise of identical results across apps or carriers.
Troubleshooting a count that does not match
- Confirm the unit. If one counter reports characters and another reports units, convert them. Each extension-table character costs two units, so a message with several
^symbols will read longer in units than in typed characters. - Find the encoding trigger. Look for curly quotes, emoji and any symbol outside the GSM alphabet. Replace curly quotes with straight quotes and retype the text. If the count drops to the GSM-7 limits, the trigger was the cause.
- Check the sending tool’s encoding setting. In an API, look for a unicode-forcing parameter such as
type=unicode. In a messaging service, look for Smart Encoding. If either is enabled, the text that arrives may differ from the text you typed. - Check where the segment boundary falls. For a single message, the limit is 160 GSM-7 units or 70 UCS-2 characters. For a multipart message, each segment holds 153 or 67. A count one unit past a boundary means one more message.
- Check the route. Toll-free numbers in the US or Canada use 152 and 66 in Twilio’s documentation. Short codes and carriers can behave differently, so ask your provider for the values for your specific route.
- Check the channel. If the recipient is on RCS, the SMS counter may not describe what was delivered, and Google Messages can fall back to SMS or MMS.
For developers, Twilio’s Message Segment Calculator and Vonage’s Messages API documentation are useful for checking how a specific provider handles encoding and segmentation.
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