What are custom segments in Google Ads, and why are they not a placement list?
Part of Google Ads placements
The short answer
A custom segment is a Google Ads audience built from keywords, website URLs or app names that describe an ideal customer. Google uses those inputs to find people with matching interests or behavior, then shows them ads wherever they browse. Entering a URL reaches people who visit similar sites; it does not place ads on that URL.
Key takeaways
- Custom segments describe people: Google turns keywords, URLs and apps into an audience estimated from browsing, app and search activity.
- Google states that adding a URL to a custom segment does not mean ads will show on that URL, which is the main difference from a placement.
- Custom segments run in Display, Demand Gen and Video campaigns, act as signals in Performance Max, and are not available in Search, Shopping or Hotel campaigns.
- Placed in the same ad group as a placement list, a custom segment narrows delivery to segment members on the listed pages.
What are custom segments in Google Ads?
Google's custom segments page (opens in a new tab) describes them as a way to reach an ideal audience by entering relevant keywords, URLs and apps. An advertiser can build one in Display, Gmail, Demand Gen and Video campaigns. Google reviews the inputs against its advertising policies, then shows ads to people with those interests or purchase intentions on pages, apps and videos.
Definition
- Custom segment
- An audience segment the advertiser defines with keywords, URLs or app names instead of choosing one of Google's ready made affinity or in-market lists. Google interprets the inputs and estimates which people fit.
The inputs are hints, not a membership list. Google says the system reads them with the campaign's goals and bidding strategy and leans toward reach, consideration or performance, so two campaigns with the same segment and different bidding can reach different people.
| Input | Who Google reaches | What Google adds |
|---|---|---|
| Keywords, as interests or purchase intentions (the default) | People likely interested in or intending to buy what the keywords describe, based on behavior such as the apps they use and the content they browse or search for | This is the default interpretation for keywords |
| Keywords, as search terms | People who searched for those or similar terms on Google properties such as Google.com and YouTube | Applies only on campaigns running on Google properties; elsewhere the terms are read as interests |
| URLs | People who browse websites similar to the URLs entered | This doesn't mean ads will show on those URLs |
| Apps | People who download and use apps similar to the ones entered | This doesn't mean ads will show on those apps |
How do URLs in a custom segment work?
Your ads will reach people who browse websites similar to the URLs you enter.
A URL in a custom segment is a description of a reader. Google treats it as a sample of the kind of site the ideal customer visits and looks for people who browse sites like it. The ad can then appear anywhere those people go within the campaign's reach: a weather app, a news homepage, a recipe site or a YouTube video. Google adds a sentence that matters for planners: this does not mean the ads will show on those URLs.
Why is a custom segment not a placement list?
A placement chooses the content and a custom segment chooses the person. Google's About placement targeting page (opens in a new tab) defines placements as locations where ads can appear on YouTube or the Google Display Network. A custom segment has no location of its own. It sits in the audience part of the account, beside affinity, in-market and your data segments, as Google's audience segments page (opens in a new tab) lists them.
| Question | Custom segment | Placement list |
|---|---|---|
| What it selects | People estimated to share interests, searches or habits | Specific websites, apps, YouTube channels or videos |
| Where ads can appear | Anywhere segment members browse within the campaign's reach | Only on the listed placements, unless other targeting widens the ad group |
| What a URL means | An example of sites the audience visits | A page or site the ad may appear on |
| Data behind it | Activity on Google products and third-party sites, estimated by Google | The publisher's content; no profile of the reader is needed |
| What it is good at | Finding a niche audience across many sites, including ones the planner never thought of | Control and review: each site can be checked for quality, suitability and selling path before money moves |
| Where it falls short | No list of where ads ran before launch; the audience is Google's estimate | Reach is capped by the list; a niche list can be small and slow to deliver |
| How to verify delivery | Audience reports and the placement report after launch | The placement report, matched to the approved list |
The placement targeting guide covers how placements combine with topics and keywords, and the lookalike audiences explainer covers audiences built from customer lists.
When should custom segments and placements be used together?
Combining them is a choice between two settings. Google's Display targeting overview (opens in a new tab) says each new targeting layer narrows potential reach, so a custom segment and a placement list in one ad group, both on the Targeting setting, serve only to segment members while they are on listed pages. Google's Targeting and Observation page (opens in a new tab) describes the second option: an audience added as Observation does not restrict reach and is reported where it overlaps existing targeting.
- List only, segment in Observation: the safest start for a brand that must stay on reviewed sites. The report then shows how the segment performs inside the list without shrinking it.
- Segment on the list, both Targeting: useful when a large list, such as general news, should reach only part of its readers. Expect slower delivery.
- Segment only: a prospecting choice. Pair it with account level placement exclusions and content suitability settings, since no reviewed list limits the pages.
- Separate ad groups: one on the list, one on the segment, so results can be read apart.
Demand Gen behaves differently. The feature table on Google's Display to Demand Gen migration page (opens in a new tab) lists custom audiences as supported but the Observation setting for non-demographics as not supported in Demand Gen, so the observe first approach needs a Display campaign or a separate test ad group. The targeting and observation guide covers the setting in detail.
What data do custom segments rely on?
Google's audience segments page says audiences are determined by people's activity using Google products and third-party websites, or estimated from content certain groups are likely to be interested in. Activity on third-party sites is mainly used for segments on third-party sites, and activity on Google products mainly for segments on Google products. For custom segments specifically, Google names the apps people use and the content they browse or search for.
Policy limits follow from that. Google's personalized advertising policy (opens in a new tab) groups custom segments with predefined Google audiences, says users under 18 are not eligible for personalized advertising of any kind, and adds that custom segments with sensitive creative or landing pages serve only in Display campaigns, to non-sensitive audiences or contextually; other campaign types with such segments are not eligible to serve. A placement list, by contrast, can run without any audience data about the reader.
How do you build a custom segment that a planner can defend?
Build and attach a custom segment
- Write the audience in one sentence. Name who the customer is and what they research, before choosing any input.
- Open Audience manager. In the Tools menu, open Audience manager, go to Custom segments and select the plus button. Manager accounts have no custom segments table, so work in the client account.
- Pick the interpretation. Leave the default for interests and purchase intentions, or choose search terms on Google when the campaign runs on Google properties such as YouTube.
- Add inputs in one theme. Use keywords, URLs and apps that describe the same person; mixing unrelated themes blurs the estimate.
- Ignore the default estimate settings. Google says Segment Insights defaults to the US and English, while the segment follows the campaign and ad group settings it is added to.
- Attach it in the ad group. In Audiences, select Edit audience segments, choose the ad group and tick the segment, then decide Targeting or Observation.
Before launching a campaign with a custom segment
- The team knows the URLs describe readers, not where ads will run.
- If the brand must stay on reviewed sites, the sites sit in placements and the segment is in Observation or narrows the list.
- Account level placement exclusions and content suitability settings are in place for any ad group without a list.
- The campaign type supports custom segments: Display, Demand Gen or Video, or Performance Max as an audience signal only.
- The creative and landing page fall outside Google's sensitive interest categories, or the plan accounts for the serving limits.
- A date is set to read the placement report and the audience report together.
What does the difference look like on a real brief?
Fictional example
A 3D printer and filament retailer in Montana and Wyoming
A fictional Bozeman retailer of desktop 3D printers, filament and spare parts asks its agency for display and video ads across Montana and Wyoming, in English. The client hands over a list of thirty maker forums, printing tutorial sites and model sharing communities its customers use.
The first draft puts the thirty URLs into a custom segment. The planner flags it: the segment would reach people who browse similar sites, on any page, and the client's list would not limit where ads appear. The client wanted both, presence on the maker sites and reach to hobbyists elsewhere.
The final plan has two ad groups. The first targets the reviewed maker sites as placements, with the custom segment added in Observation. The second targets the custom segment alone, with keywords about printer upgrades and filament types, protected by account level exclusions. The placement report is read by ad group, so on-list and off-list delivery stay separate.
How does PlacementGraph fit a plan that uses custom segments?
Frequently asked questions
Can a custom segment be shared across Google Ads accounts?
No. Google says custom segments are not shareable from one account to another, and a manager account has no custom segments table in its audience manager. An agency running several client accounts builds the segment in each one, which is a good moment to adapt the inputs to each client's audience.
Can custom segments be used in Performance Max?
Not as targeting. Google says custom segments cannot be applied directly to Performance Max, but they can be added to an audience signal in an asset group, and Google suggests search term based segments there. Performance Max may still show ads to people outside the signals when they are likely to convert.
Do custom segments work in Search campaigns?
Google's audience segments table lists custom segments as available in Demand Gen, Display and Video campaigns and not in Search, Shopping or Hotel campaigns. The search terms option is about past searches on Google properties used to reach people in other campaign types, not about serving Search ads.
How many inputs should a custom segment have?
Google's custom segments help page publishes no minimum. Coherence matters more: inputs that describe one kind of person give a clearer signal than a long mixed list, and several focused segments, each in its own ad group, are easier to read in reports.
Sources
- About custom segments (opens in a new tab)Google Ads Help
- About audience segments (opens in a new tab)Google Ads Help
- About placement targeting (opens in a new tab)Google Ads Help
- About targeting for Display campaigns (opens in a new tab)Google Ads Help
- About Targeting and Observation settings (opens in a new tab)Google Ads Help
- Google Display Ads campaigns have a new home in Demand Gen (opens in a new tab)Google Ads Help
- Personalized advertising (opens in a new tab)Google Advertising Policies Help
- About audience signals for Performance Max campaigns (opens in a new tab)Google Ads Help
Researched and written by PlacementGraph Research. Read how we research, source and update these pages. Corrections: diana@placementgraph.com.