Understanding SMS character limits

When drafting an SMS in Instant, you'll see a character counter showing 120/120 at the start. This article explains where that limit comes from, what counts toward it, and why the count can change as you type.

This applies to SMS in campaigns. SMS in flows is generated automatically by Instant and stays within the same limit, so there's nothing to manage on your end.

Why we manage your character count

Behind the scenes, SMS has a strict set of technical rules that decide how many credits a single message costs and how it arrives on a shopper's phone. Get them wrong and a message can be split into multiple parts, billed multiple times, arrive out of order, or look unprofessional.

Instant takes care of all of that for you. Your counter shows you exactly how much room you have, accounts for the encoding rules automatically, and reserves space for the things that legally have to be in every commercial SMS. That means:

Predictable cost. One SMS sent = one credit charged. You'll never accidentally pay for a multi-part message.
Clean delivery. Every message arrives as a single SMS, in one piece, exactly as you wrote it.
Compliance built in. Your unsubscribe line is added automatically, so you can't forget it.
Less to think about. You don't need to understand SMS encoding rules. The counter tells you what you have, and the editor enforces the rest.

The rest of this article explains how the counter works so you can write messages that make the most of the space available.

Why 120 characters?

A standard SMS holds 160 characters when sent in the default character set. Instant reserves the remaining 40 characters for two things that send automatically with every message:

The link (a shortened URL is added at the end)
The Reply STOP to unsubscribe line (required by law in Australia)

That leaves 120 characters for your prefix and message body. By keeping every send within a single SMS, your messages always cost one credit each, regardless of length.

What counts toward your 120 characters

Your brand prefix (set in SMS Settings)
The message body you type
Variables like first name (more on this below)
Spaces, punctuation, line breaks

What doesn't count toward your 120 characters

The link at the end of the message
The Reply STOP to unsubscribe line
The line breaks between your message, the link, and the STOP line

So if your prefix is EM'S:, you start with 6 characters used and 114 remaining for the body. If your prefix is AFTERSHOCK:, you start with around 11 characters used and 109 remaining.

A shorter prefix gives you more space for your message. If you want to maximise message length, the short prefix option is the way to go.

Why your character count can change as you type

Standard SMS messages are encoded in a character set called GSM-7, which fits 160 characters per message. As soon as you include a character outside that set (emojis, curly quotes, accented letters, Chinese or Arabic characters), the message switches to a different encoding called UCS-2, which only fits 70 characters per message.

To keep your sends to one SMS per recipient (and one credit), Instant automatically calculates which encoding your message uses and reduces your available character count if needed. So if you add an emoji, you'll see your remaining characters drop. Remove it and the count goes back up.

You don't need to think about the encoding itself, just keep an eye on the counter.

How variables affect your character count

When you add the First name variable, Instant reserves 7 characters in your count to account for the name being inserted at send time. This covers most first names without going over.

When the SMS actually sends:

If the shopper's name is 7 characters or shorter, their name is inserted directly.
If their name is longer than 7 characters, your fallback is used instead.
If the shopper has no first name on file, the fallback is used.

This is why setting a fallback is important. It's not just for unknown contacts, it's also what gets used when someone's name is too long to fit. A short, friendly fallback like there or friend works well.

Example: With a fallback of there, the message "Hi {First name}!" sends as "Hi Sam!" to a shopper named Sam, but "Hi there!" to a shopper named Christopher.

Tips to maximise your character count

Pick the short prefix option in SMS Settings if you want more room for your message.
Avoid emojis and special characters unless they're essential. They shrink your limit significantly.
Use straight quotes (' and ") instead of curly quotes (' and "). Curly quotes count as special characters.
Keep your fallback short. A 5-character fallback like there saves more space than friend (6) or valued shopper (14).