SMS Segments Explained: Why Your Text Message Costs More Than You Think

A 200-character text message doesn't cost one message — it costs two. SMS billing is based on segments, not messages, and the math changes completely the moment your text switches encoding. Here's exactly how carriers and SMS platforms calculate what you pay.

Segments, Not Characters, Determine Cost

Every SMS provider — from carriers like Verizon and AT&T to gateways like Twilio and MessageBird — bills per segment. A segment is a single 160-character (GSM-7) or 70-character (Unicode) chunk. Text longer than one segment is automatically split into multiple parts by your phone or the sending platform, and you're billed for each part individually.

Segment Breakdown Table

For the complete interactive reference with all fields for every platform, visit our all-platforms character limit cheat sheet — with 16 platforms in one page and links to dedicated tools for each.

Why 153, Not 160, for Multi-Part Messages

Once a message needs to split, each segment sacrifices a small amount of space (7 characters under GSM-7, 3 under Unicode) for a User Data Header (UDH). The UDH tells the receiving phone the order to reassemble the parts in and which message they belong to. That's why a 2-segment GSM-7 message tops out at 306 characters (153 × 2), not 320.

A Real Example of Silent Cost Doubling

Consider a 155-character promotional text — well under the 160-character single-segment limit. If that text includes one curly apostrophe (auto-corrected by a word processor) or a single emoji, the encoding silently switches to Unicode. At 155 characters, a Unicode message needs three segments, not one — a 3x cost increase with no visible change to the text itself.

How to Avoid Accidental Multi-Segment Billing

• Write and paste into plain-text fields, not rich-text editors that auto-convert straight quotes to curly ones
• Run copy through a character counter that flags encoding before you send, not after
• If your brand voice requires emoji, budget for 70-character segments from the start rather than 160
• For bulk SMS campaigns, test a sample message through your gateway's preview tool before a full send

These are the same encoding mechanics behind the 160 vs 70-character SMS limit — this article focuses specifically on what that means for your bill.

See our SMS marketing best practices guide for copy strategy, or compare against MMS limits if you're sending images. For other tightly-billed character fields, see Google Ads Quality Score, the social media character limits guide, and our Twitter/X character limit guide. Amazon sellers running SMS cart-recovery flows may also want our Amazon backend keywords guide.