When creating a Google Ads campaign, the number of keywords you should include in an ad group is an important aspect of your strategy. The key is to strike a balance between relevance and optimization, ensuring your ads target the right audience without overloading your ad groups with too many keywords.

General Best Practices for Keywords in Google Ads Ad Groups:
5-20 Keywords per Ad Group:

Best Practice: Google recommends keeping each ad group between 5 and 20 keywords. This allows you to maintain relevance while ensuring enough search volume to generate meaningful results.

Focused and Specific: Having fewer, highly relevant keywords ensures that the ads are tailored more precisely to the user's search intent, which can increase your Quality Score and improve ad performance.

Thematic Grouping:

Group your keywords based on common themes. For example, if you're selling shoes, create separate ad groups for "running shoes," "leather shoes," "women's shoes," etc. Each ad group should contain keywords that relate directly to the specific product or service you're advertising.

Match Types Considerations:

Broad Match: If you're using broad match keywords, you may need fewer keywords in the ad group, as these keywords will cover a wider array of search terms.

Exact and Phrase Match: For more precise targeting, use exact and phrase match keywords, which would warrant a smaller number of highly specific terms in the ad group.

Avoid Keyword Cannibalization:

Don't add the same keyword across multiple ad groups, as this can cause your ads to compete against each other, reducing overall campaign performance. Each ad group should be distinct with a unique set of keywords.

Quality Over Quantity:

It's better to have a smaller number of highly relevant keywords that match well with your ad copy, landing page, and audience intent than to overload the ad group with dozens of loosely related keywords.

Ad Group Structure for Larger Campaigns:

For larger campaigns, you might have several ad groups with 5-20 keywords each, organized by theme or product category. This organization helps Google deliver more relevant ads and improves the overall campaign performance.

Additional Tips:
Use Negative Keywords: To ensure that your ads don't show for irrelevant searches, make sure you add negative keywords to filter out unwanted traffic.

Refining with Search Terms: Over time, analyze the search terms report to discover new keywords to add to your existing ad groups and remove irrelevant ones.

Conclusion:
Typically, keeping 5 to 20 keywords per ad group is ideal, but the key is relevance. The more focused and relevant your keywords are to your product or service, the better your chances for improving your Quality Score, ad relevance, and overall campaign performance.