Meta's Business Help Center still says a customer list should include at least 1,000 customers. The 100-person number you'll hear is a different rule: Meta's Marketing API says a custom audience needs at least 100 people to seed a lookalike, with at least 100 from one country unless you allow international seeds. You'll also hear that Meta cut its customer list minimum from 1,000 to 100. We couldn't find that change on any Meta page, and its own formatting guidelines say otherwise.
The three numbers people mix up
- Uploading a list. Meta's formatting guidelines say a customer list should include at least 1,000 customers, plus at least one main identifier. Not everyone on it will match, and low match rate gets its own status, so send more than one identifier per person: Meta says multiple keys raise the match rate. Changes usually take up to 24 hours to apply.
- Running ads to it. The audience's delivery status is the answer: 200 means active and ready, 300 means too small, inactive and unusable.
- Seeding a lookalike. At least 100 people in the source and at least 100 from a single country, or 100 unique conversions if you seed from campaigns or ad sets, with 200 or more converters recommended.
So "100" is a lookalike rule, and 1,000 is what Meta asks for in the list. To know whether your list will deliver, check its status after the upload instead of trusting a number you heard. And if you plan to build a lookalike from it, the seed matters more than the size, as we cover in a lookalike only copies the seed you feed it.
Where a small list earns its place: behind outbound
On a mentoring call, we looked at a lead generation agency that sells to construction technology startups in the US. The market was roughly 2,000 to 3,000 companies. At three decision makers each, that's 6,000 to 8,000 people at most. We didn't recommend Search for a market that narrow, and for an audience that small LinkedIn is far more expensive.
Our suggestion: keep emailing and messaging all of them on LinkedIn, upload the same list to Meta, and keep a small campaign showing your videos and images to only those people. When the email lands, the name already feels familiar. That's brand recall, and we were direct about it on the call: with a base that small, the ads are mostly branding, clicks will be expensive, and you shouldn't expect a flood of form fills. We put a Meta campaign at around $1,000 a month. The LinkedIn version of this play, with LinkedIn's 300-member floor, is in warm the list with a LinkedIn ad before the first cold email.
Two things that break it
- Expansion. Meta's documentation says Advantage custom audience is on by default for supported objectives, and Advantage+ audience only holds location, minimum age, language and custom audience exclusions fixed. Your list inclusion isn't on that list. Turn expansion off or set the audience as a control, as in suggestions vs controls, or the list-only campaign isn't list-only.
- Saturation. A few thousand people see your ads fast. Our read on that call: it works for one or two months, not three or more. If the list still isn't talking to you after two months of seeing you, the market is saturated, and the next step is a bigger market, not more spend.
The takeaways
- Meta's Help Center says a customer list should include at least 1,000 customers. We found no documented cut to 100.
- The 100 is the minimum lookalike source: 100 people, at least 100 from one country.
- After upload, read the delivery status: 300 means too small to use.
- A small B2B list on Meta works as recall behind email and LinkedIn outreach, not as a lead engine.
- Switch off expansion to stay on the list, and expect saturation within one to two months.
Common questions
What is the minimum size for a Meta custom audience?
Meta's Business Help Center formatting guidelines say a customer list should include at least 1,000 customers. Once uploaded, each audience also has a delivery status: 200 means it is active and ready to use, and 300 means it is smaller than it should be, inactive and can't be used. Check the status after your upload has processed.
What is the minimum source size for a Meta lookalike audience?
Meta's Marketing API says the source custom audience needs at least 100 people, and at least 100 seed members from one country unless you allow international seeds, which is off by default. A lookalike seeded from campaigns or ad sets needs at least 100 unique conversions, and Meta recommends 200 or more converters.
Did Meta lower its custom audience minimum from 1,000 to 100?
Not according to Meta's own pages. Its customer list formatting guidelines still say a list should include at least 1,000 customers. The 100 figure Meta documents is the minimum source size for a lookalike audience, which is likely where the mix-up comes from.
Will Meta show my ads only to my custom audience?
Not by default in many setups. Meta's documentation says Advantage custom audience is enabled by default for supported objectives, and Advantage+ audience only treats location, minimum age, language and custom audience exclusions as fixed constraints. To keep delivery on your list, turn the expansion off or set the custom audience as a control.
How do I get more of my list to match on Meta?
Send more than one identifier per person. Meta's customer file documentation says providing multiple keys increases the match rate, and it flags a low match rate as its own audience status. Changes to a custom audience usually take up to 24 hours to apply, so check the size the next day.