What is an SMS segment?
An SMS segment is one slice of a text message, up to 160 plain characters, that mobile networks count as a single unit. A longer text is split into several segments and joined again on the phone. Knowing the limits helps you keep each alert to one.
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Published:
Plain letters, numbers and common symbols: 160 characters fit in 1 credit.
How SMS segments are counted
Most alert texts use GSM-7, the basic character set with English letters, digits and common symbols. A GSM-7 text holds 160 characters in one segment. Once split, each part holds 153, because a few characters stitch the parts together.
Unicode is the larger set that covers emoji and curly quotes. A Unicode text holds 70 characters alone, or 67 per part once split.
Why one emoji can double the count
The network picks one character set for the whole text. A single emoji or smart quote moves every character to Unicode, so the 70 limit applies. An alarm that fit in one segment can suddenly need three.
Smart quotes often slip in when alarm wording is typed in a word processor. Straight quotes keep the text in GSM-7.
A long alarm and its trimmed version
The first text below runs to 208 plain characters, so it goes out as two segments. The trimmed one keeps the filter, the reading and the time in a single segment of 76 characters.
- Raw alarm email, sent as is (2 segments): Welco: FW: Alarm Notification. Site: North Plant. Group: WTP. Tag: FLT3_TURB. Desc: Filter 3 effluent turbidity HIGH. Value: 0.62 NTU. Event: ALM. Ack: NO. Time: 10/06/2026 02:14:55 AM. Reply STOP to opt out.
- Same alarm after a trim rule (1 segment): Welco: [Filter 3] Turbidity HIGH 0.62 NTU at 2:14 AM. Reply STOP to opt out.
What segments mean for your alert texts
Each segment sent to each phone uses one message credit. Very long alerts use more credits unless you trim them, and emoji make a text cost more too.
Welco can cut alert emails down to one text by keeping only the lines that matter. For worked examples and a character table, see SMS segments explained.
SMS segment vs character limit vs carrier filtering
People mix these up when a text looks wrong. The character limit is the size of one segment. A segment count is how many slices one text needed.
Carrier filtering is a separate thing. A filter can block a short text just as easily as a long one. Both terms sit side by side in the SMS alert glossary.
Frequently asked questions
How many characters fit in one SMS segment?
Is one SMS segment the same as one message credit?
How much room is left for the alarm itself?
Welco: and ends with the opt-out line with STOP, which carriers require. Together they use roughly 30 of the 160 characters.Which characters push a text into Unicode?
Keep every alarm text inside one segment
Set a trim rule once and each alert arrives as one short text.
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