A custom segment is a Google Ads audience you build yourself by listing keywords, website addresses or apps that describe the people you want to reach. Google then finds people whose searches, browsing or app use match that description and shows them your ads. It replaced the older custom intent and custom affinity audiences.
How a custom segment works
You create the segment in the Audience manager or while editing a campaign’s audiences. You add interests or behaviours as keywords (for example “loft conversion” or “garden office planning permission”), URLs of websites your customers are likely to read, and apps they might use. You can also choose to target people who searched for any of your keywords on Google, which makes the segment much closer to search intent.
Google treats URLs and apps as descriptions of a type of person, not as placements. Adding a competitor’s domain does not put your ads on their site; it tells Google to find people with interests similar to those who visit it. The segment is then used in campaigns such as Display, Video and Demand Gen, and as an audience signal in Performance Max.
Custom segments sit alongside Google’s ready-made affinity audiences and in-market audiences. Those are built by Google and are broad by design. A custom segment is yours, so it can describe a niche that no ready-made list covers. The name causes confusion with Meta: a “custom audience” on Facebook is a list of your own customers or visitors, which in Google Ads is closer to Customer Match or remarketing.
Why it matters
On YouTube and display placements there are no search queries to target, so audience choice decides who sees your ads. Ready-made segments are often too broad for a UK small business. A Bristol company selling commercial kitchen extraction will not find many buyers in an in-market segment for “home and garden”, but a custom segment built from searches such as “commercial kitchen ventilation regulations” and the websites of trade catering suppliers describes its buyers far more closely.
In Performance Max, a well-built custom segment helps the system find the right people sooner, which matters most in the first weeks when it has little conversion data.
Common mistakes
- Adding a handful of very broad keywords, such as “marketing” or “business”, which produce an audience too vague to help.
- Expecting a competitor URL to place ads on that competitor’s website.
- Mixing unrelated themes in one segment, so you cannot tell which idea is working.
- Assuming that because a segment is attached, the campaign only reaches those people, when optimised targeting may be expanding beyond it.
- Building a segment once and never checking which placements or viewers it actually brought.
How to act on it
Write your segment from what you know about real customers. Pull keywords from your search terms report on converting searches, add the trade websites and publications your buyers read, and keep each segment to one theme. Ten to thirty specific terms usually beat a long list of loose ones.
In Performance Max, add your strongest segment as a signal and treat it as a starting hint: the campaign will still reach people outside it, so judge it on conversions rather than on how closely the audience matches your list.
Test it in a campaign with conversion tracking in place, compare it against a ready-made segment, and look at where the ads ran. Refine the terms every few months. Building audiences like this is central to how I plan YouTube advertising campaigns.