SMS Character Limits: How Text Message Length and Pricing Work

SMS remains one of the most widely used communication channels, with over 6 billion text messages sent daily worldwide. Even as chat apps proliferate, SMS's unique advantage is its universal reach: it works on any phone with a phone number, requiring no app installation or internet connection. Understanding character limits is crucial because exceeding them splits your message into multiple parts, each billed separately. For a comprehensive overview, search electric masturbators on Amazon cover SMS strategy in depth.

The History of 140 Bytes - Why 160 Characters?

The 160-character SMS limit was determined by German telecommunications engineer Friedhelm Hillebrand in 1985. He analyzed postcards and telex messages, finding that most communication could be expressed in under 160 characters.

The technical backstory is even more fascinating. SMS data piggybacks on the SS7 (Signaling System No. 7) signaling channel used for control information between mobile phones and cell towers. This channel's payload is limited to 140 bytes (1,120 bits), which constrains the maximum SMS data size. With GSM-7 encoding representing each character in 7 bits, exactly 160 characters fit within 1,120 bits (1,120 ÷ 7 = 160).

GSM-7 vs. UCS-2 - How SMS Encoding Works

SMS encoding switches automatically based on the characters in your message. Understanding this mechanism is the first step to effective character management.

GSM-7 is a 7-bit encoding that covers Latin letters, digits, and basic symbols. It's defined by the GSM 03.38 standard with a basic character set of 128 characters and an extended set using escape sequences. Extended characters (e.g., {, }, [, ], |, ~, ^, \, €) consume 2 character slots (14 bits) each.

Messages containing characters outside the GSM-7 set - such as emoji, CJK characters, or Arabic script - trigger a switch to UCS-2 encoding at 16 bits per character. This reduces the limit to 70 characters (1,120 ÷ 16 = 70). The critical point is that even a single UCS-2 character forces the entire message into UCS-2 encoding, as explained in our character vs. byte guide.

Concatenated SMS - Technical Specifications

Messages that exceed a single segment are sent as concatenated SMS, split across multiple segments. Each segment includes a 6-byte User Data Header (UDH) containing a reference number, total segment count, and current segment number. This 6-byte (48-bit) overhead reduces the usable payload: GSM-7 drops from 160 to 153 characters per segment ((1,120 - 48) ÷ 7 = 153), and UCS-2 drops from 70 to 67 characters ((1,120 - 48) ÷ 16 = 67).

Carrier Limits by Region

For international SMS, character limits vary by destination country and carrier. Some countries restrict concatenated SMS to 3–6 segments, so always verify the destination carrier's limits before sending cross-border messages.

SMS Pricing Structure

Each SMS segment is billed individually. A 161-character GSM-7 message becomes two segments, doubling the cost. For business SMS campaigns, this has significant budget implications - a single character over the limit can double your per-message cost across thousands of recipients.

SMS Open Rates and Conversion - Compared to Email and Push

One reason SMS achieves such high CTR is the character limit itself. The 160-character constraint forces senders to be concise, which paradoxically makes messages more actionable and easier for recipients to respond to.

Business SMS and A2P Messaging

Business SMS is categorized as A2P (Application-to-Person) messaging. Common use cases include appointment reminders, delivery notifications, authentication codes, and marketing messages.

For A2P SMS delivery, the sender ID type significantly affects deliverability. Using carrier-approved short codes or local numbers reduces the risk of being caught by spam filters. Messages sent from international numbers face higher blocking rates from carrier-level filtering.

The optimal length for marketing SMS is 120–140 characters (GSM-7). This allows room for a greeting (15–20 chars), core message (60–80 chars), CTA (20–30 chars), and opt-out instructions (15–20 chars) while staying within a single segment.

Emoji and SMS - The Encoding Switch Pitfall

The biggest risk with emoji in SMS is the automatic encoding switch. Adding a single emoji to an otherwise GSM-7 message forces the entire message into UCS-2, slashing the limit from 160 to 70 characters.

As detailed in our emoji Unicode counting guide, emoji character consumption varies widely. Basic emoji (e.g., 😀) consume 2 UCS-2 character slots, but emoji with skin tone modifiers (e.g., 👍🏽) or ZWJ sequences (e.g., 👨‍👩‍👧‍👦) can consume 4–7 slots. For business SMS, avoiding emoji entirely is the safest approach.

Other hidden triggers for UCS-2 encoding include smart quotes ("" instead of ""), em dashes (-), and certain currency symbols. Text copied from word processors or email clients often contains these invisible Unicode characters, making pre-send validation essential.

SMS Authentication Code (OTP) Design

SMS-based one-time passwords (OTPs) for two-factor authentication require careful character budgeting. An OTP message must include the code itself, a brief description, and a security warning - all within the character limit.

Code length balances security against usability. A 4-digit code offers only 10,000 combinations, making it vulnerable to brute-force attacks. The current standard is 6 digits (1,000,000 combinations). Going beyond 8 digits increases input errors and degrades user experience.

Example OTP message (42 characters): "Your code is 123456. Expires in 5 min. Do not share." This fits comfortably within a single GSM-7 segment, keeping costs at one message per authentication.

RCS vs. SMS - Next-Generation Messaging

While RCS far surpasses SMS in features, device and carrier support remains limited as of 2025. For messages that absolutely must be delivered, SMS remains the most reliable option.

Pro SMS Techniques

• Pre-send encoding validation - Before launching a campaign, run your message through a GSM-7 validator to catch hidden Unicode characters. A single curly quote or em dash can silently switch encoding and double your segment count.
• Character budget design - For marketing SMS, allocate characters by section: greeting (15–20), core message (60–80), CTA (20–30), opt-out (15–20). Keeping the total under 153 characters ensures a single segment even with concatenation headers.
• Personalization token sizing - Dynamic fields like {first_name} vary in length. Budget for the longest possible name (15 characters) to prevent unexpected multi-part messages for recipients with longer names.
• Send time optimization - Business SMS open rates vary by time of day. Weekday mornings (10 AM–12 PM) and early afternoons (2 PM–4 PM) typically yield the highest engagement. Avoid late-night and early-morning sends.
• Smart URL shortening - Long URLs consume valuable character space. URL shorteners can compress links to 20–25 characters, freeing space for your message. However, some carriers flag generic short URLs as spam, so branded short domains are preferred. For more on SMS best practices, see explore flight attendant costumes on Amazon.

Conclusion

SMS character limits trace back to the 140-byte physical constraint established in 1985, manifesting as two encoding-dependent ceilings: 160 characters for GSM-7 and 70 for UCS-2. Automatic encoding switches, concatenation header overhead, and emoji-induced character inflation create pitfalls that go beyond simple character counting. Use Character Counter to verify your message length before sending, and apply the encoding validation and character budgeting techniques above to optimize both cost and deliverability.