Google RSA character limits: the numbers, the traps, and why AI copy still breaks them

Google RSA character limits are 30 characters per headline, 90 per description and 15 per display path field, with 3 to 15 headlines and 2 to 4 descriptions in each responsive search ad. Characters in Chinese, Japanese and Korean count double. The numbers have been stable for years; what changes is who writes the copy. With AI Max and other tools now drafting headlines automatically, the limits are worth stating precisely, in the brief and in the prompt.

Google RSA character limits at a glance

These figures come from Google's help page on responsive search ads.

Each ad shows at least one headline and one description, and up to three headlines can appear in the headline position. Headline 1 and Description 1 usually show; Headline 2, Headline 3 and Description 2 may or may not. Google recommends at least two responsive search ads per ad group rated Good or Excellent on Ad Strength.

Three traps in the RSA character limits

Double-width characters count as two

Every character in a double-width language such as Chinese, Japanese or Korean counts as two. A Japanese headline therefore holds 15 characters, not 30. Teams that localise English copy by character count alone will produce headlines Google rejects.

The specs page has a second, shorter headline limit

Google's Search campaigns specs page shows two tables. The responsive search ad table gives headlines of up to 30 characters. A general ad assets table on the same page lists headlines of up to 25 characters. Use 30 for RSAs, but check which table applies before you set a limit in any tool that writes copy for other formats.

Fitting the limit is not the same as showing

A headline can be within 30 characters and still never appear. Only pinned positions are guaranteed, and Google says pinning cuts the number of combinations it can test, so it does not recommend pinning for most advertisers. If a claim must always show, such as a legal line, pin it, and accept the trade-off.

How to check RSA headline length before upload

Finding an over-length headline in the editor is slow when you have dozens of variants. A short script catches it earlier, including the double-width rule:

import unicodedata

LIMITS = {"headline": 30, "description": 90, "path": 15}

def google_length(text):
    # Wide and full-width characters count as two, as Google counts them.
    return sum(2 if unicodedata.east_asian_width(c) in ("W", "F") else 1 for c in text)

def check(field, text):
    n = google_length(text)
    return n <= LIMITS[field], n

print(check("headline", "Free delivery on every order"))  # (True, 28)
print(check("headline", "全国送料無料キャンペーン実施中です"))  # (False, 34)

Run it over every generated variant before anything reaches Google Ads. It is a fact check, so it does not need a model at all.

Why AI-written ad copy still breaks character limits

Language models do not see characters the way Google counts them; they work in chunks of text, so length is something they estimate rather than measure. Our own measurements show what helps and what does not.

On caption writing, staying within a platform's length limit, the untrained base model scored 0.89 when the limit was stated in its instructions. Our fine-tuned version, trained on examples instead of told the rule, scored 0.83. Training a model on a limit made it worse at following the limit. We cover the full result, four tasks out of five where prompting beat training, in when to fine-tune an LLM, and the raw numbers sit in our build log.

We also retracted a claim here, and it is worth repeating. An earlier version of our status file reported 0.947 for writing ads to exact Meta, Google RSA and TikTok constraints. The evaluation was broken: it sent the model the correct answer alongside the brief. Measured properly, the fine-tune scored 0.04, the same as the untrained base. So the practical rule is twofold: state the limits in the prompt, and verify lengths with code afterwards, because neither a prompt nor a model guarantees them.

The same applies to copy Google writes for you. AI Max can generate headlines, and Google's reporting now shows which search terms they served, as we described in our post on Google AI Max. Length is Google's concern there; claims and brand are still yours, and no character count can check those.

Where gloofy fits, and where it does not

Building now Writing ads to exact platform constraints (Meta, Google RSA and TikTok) is a task we are building, listed under what gloofy does. It is not shipped, and its last honest measurement was 0.04, no better than the base model. We are not claiming it works yet.

What we can say from measurement is how to get there: the limits go in the prompt as facts, and a script like the one above checks the output. A model is for the part a rule cannot capture, such as which angle to lead with. Other platform rules of this kind, from safe zones to policy, collect in the platform specs and compliance hub.

What to do this week

• Put the exact limits (30, 90, 15, and double-width counting) in every prompt and brief that produces search ad copy.
• Run a length check over every generated headline and description before upload.
• For Chinese, Japanese and Korean campaigns, budget 15 characters per headline, not 30.
• Pin only what must always show, and review Ad Strength after pinning.
• Review AI Max-written headlines for claims, since a character count says nothing about whether a claim is true.

FAQ

What are the Google RSA character limits?

Responsive search ad headlines can be up to 30 characters, descriptions up to 90 and each of the two display path fields up to 15. Each ad needs at least 3 and can have up to 15 headlines, and needs at least 2 and can have up to 4 descriptions. Double-width characters count as two.

Do Chinese, Japanese and Korean characters count double in Google Ads?

Yes. Google counts every character in a double-width language such as Chinese, Japanese or Korean as two characters. A responsive search ad headline in Japanese therefore fits about 15 characters, and a description about 45. Check localised copy with a counter that applies this rule before uploading.

How many headlines show in a responsive search ad?

Each ad shows at least one headline and one description, and up to three headlines can appear in the headline position. Headline 1 and Description 1 usually show, while Headline 2, Headline 3 and Description 2 may not. Pinning guarantees a position but reduces the combinations Google can test.

Can AI write ad copy that fits RSA character limits?

It can help, but do not rely on it. Models estimate length rather than count it. In our tests, stating the limit in the prompt worked better than training a model on it, and a model fine-tuned for platform constraints scored no better than its base. State the limits, then check every output with code.