Audience Targeting

Custom Segments vs Topics Targeting: Defined Behavior or Broad Content Category

In short: Both help you reach Display or video inventory without a search query, but they work on different objects. Custom segments describe a person's behavior across sites and apps, built from inputs you supply. Topics targeting places ads on pages and channels Google classifies under a subject you pick from its topic tree, targeting content, not a person's history. Topics are fast to set up but wide by design; custom segments take more effort but stay closer to the exact behavior you want. Pick topics for quick, broad contextual coverage, and pick custom segments when you need the audience defined more precisely than any topic node allows.

By the AdFlint research team · Fact-checked against current Google and Meta platform behavior · Last reviewed July 2026

Custom Segments

Lets you define your own Google audience from keywords people search, websites they browse, or apps they use, instead of picking a prebuilt segment.

You supply search terms, URLs, or app IDs, and Google assembles an audience of people whose behavior matches those signals across Display, Video, and Demand Gen. It is the closest thing to keyword targeting outside Search, and it replaced the older custom affinity and custom intent segments. Most accounts overload one segment with unrelated inputs, which blurs the signal Google builds against.

Full definition

Topics Targeting

Places Display or video ads on pages and channels about a chosen subject, targeting the content being consumed rather than the person consuming it.

You pick from Google's topic tree and your ads become eligible on any inventory Google classifies under that topic, at whatever depth you select. It is a fast way to get broad contextual coverage across the Display Network or YouTube. Because topics are wide by design, they pull in far more inventory than expected, so placement exclusions and a capped budget keep the waste visible.

Full definition

Side by side.

The differences that actually change what happens in your account.

 Custom SegmentsTopics Targeting
What it targetsA person, based on behavior signals you describe.Content, based on Google's classification of a page or channel.
How you set it upWrite keywords, URLs, or app IDs.Select nodes from Google's prebuilt topic tree.
Typical breadthAs narrow or broad as your inputs make it.Wide by design, since topic nodes cover whole subject categories.
Where it can driftInto unrelated inventory if inputs are unrelated to each other, blurring the intended signal.Into loosely related content the topic node technically covers but you didn't intend.
Control mechanismRefine or narrow the keywords, URLs, or apps you supply.Placement exclusions and a capped budget to contain the reach.
Setup effortHigher, you're writing the defining inputs yourself.Lower, pick a node and you're targeting immediately.
Follows the person or the pageThe person, across whatever site they're on.The page, regardless of who's reading it.

What actually separates them.

01

Custom segments follow a person based on described behavior, while topics targeting follows the page or channel's classification regardless of who's viewing it.

02

Topics targeting is set up by picking from Google's existing topic tree in minutes, while custom segments require you to write and refine the keywords, URLs, or apps that define the audience.

03

Topics are broad by design and typically need placement exclusions to control drift into loosely related inventory, while custom segments narrow or widen based on how specific your own inputs are.

04

Overloading a custom segment with unrelated inputs blurs the person-level signal, while picking too broad a topic node pulls in whole categories of content you didn't intend, a different kind of drift with a different fix.

05

Custom segments can layer with Video and Demand Gen for person-based reach, while topics targeting is specifically about which content the ad appears next to and carries no behavioral history the way a segment does.

Which one should you use?

Use Custom Segments when

  • You need the audience defined by behavior, not by the topic of the page they happen to be on.
  • A relevant topic node doesn't exist or is too broad for what you're trying to reach.
  • You're willing to write and refine specific inputs to get a tighter match.
  • You want an audience that follows the person across different kinds of content, not tied to one subject.

Use Topics Targeting when

  • You want fast, broad contextual coverage across the Display Network or YouTube without building a custom audience.
  • The content itself matters more than who's reading it, you want to be near a subject, not a person type.
  • You're comfortable managing drift with placement exclusions and a capped budget rather than tight inputs.
  • You need topical coverage that a single custom segment can't easily replicate at scale.

Common questions.

Why is my topics targeting campaign showing up on unrelated pages?

Topic nodes are wide by design and cover whole categories of content, so pages you'd consider unrelated can still fall under Google's classification of that topic. Placement exclusions and a capped budget are the standard way to keep the waste visible and contained rather than expecting the topic itself to be narrow.

Can I combine custom segments with topics targeting?

Yes, both are separate targeting methods that can sit in the same Display or Video ad group. That lets you layer a behavior-based audience on top of or alongside content-based topic coverage.

Which one is better for a brand-new product with no search history?

Topics targeting tends to get inventory flowing faster since it doesn't require you to define behavior signals from scratch, while a custom segment takes more upfront thought about what terms, sites, or apps actually describe your buyer. Many advertisers start broad with topics and layer in a custom segment once they know more about who's converting.

Does topics targeting use keywords like content keyword targeting does?

No, topics targeting works from Google's predefined topic tree, while content keyword targeting works from freeform terms you write yourself that Google scans pages for. Both are content-based rather than person-based, but topics is a fixed taxonomy and content keywords are custom text.

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