What are the four kinds?
Meta builds custom audiences from four sources (Meta Business Help Centre, "About custom audiences"), and each one answers a different question.
| Source | Who ends up in it | What it is for |
|---|---|---|
| Customer list | The people on a spreadsheet you upload: emails, phone numbers, names | Reaching past customers, excluding them, or seeding a lookalike |
| Website | Visitors the Pixel or the Conversions API saw, for a window of up to 180 days, filtered by what they did | Retargeting people who looked and did not buy |
| App | People who opened or used your app | Rare for an owner-led business |
| Engagement | People who interacted with your page, posts, videos, lead forms or Instagram account, for up to 365 days | Warm audiences for businesses whose website gets little traffic |
The engagement kind is the one most owners overlook. A business that posts on Instagram and gets 300 people watching each reel has a warm audience of several thousand without a Pixel, and an ad to the people who watched more than half a video costs a fraction of an ad to strangers.
How does an uploaded list stay private?
Meta hashes it. Before the spreadsheet leaves your browser, every email and phone number is run through a one-way function that turns it into a fixed string of characters. Meta receives the strings, runs its own account details through the same function, and keeps only the matches. Meta's documentation (Meta Business Help Centre, "Customer list custom audiences and hashing") describes the process; the practical effect is that Meta learns which of your customers already have accounts and nothing about the ones who do not. The match rate is usually between 40 and 60 percent, which is why a list of 2,000 becomes an audience of 900.
Which audience should a business build first? (example figures)
A Geelong gym with 480 members and a cancelled-member list of 310 wants two things from a $900 a month Meta budget: win back some of the people who left, and find new members without paying to reach the ones it has.
| Audience | Built from | Used as | Month one (example figures) |
|---|---|---|---|
| Cancelled members | Customer list, 310 people, 170 matched | A win-back ad: come back for a month at half price | $180 spent, 9 rejoined at $20 each |
| Current members | Customer list, 480 people, 260 matched | Excluded from every acquisition campaign | $0 wasted showing joining offers to people who already pay |
| Lookalike of current members | The 260 matched members as the source | The audience for the new-member campaign | $720 spent, 14 new members at about $51 each |
The exclusion is the line most owners skip, and it is the cheapest one in the table. Without it, a share of the $720 would have shown a joining offer to people already paying $25 a week, and some of them would have asked why they were not getting it.
What does Cora do with custom audiences?
CoraVision reads your Meta campaigns and ad sets every night once Meta is connected, with their spend and results, so an ad set aimed at a win-back list and one aimed at a lookalike show their own cost per result on your dashboard. Building the audiences, uploading a customer list and setting the exclusions are steps Mira, the Meta Ads specialist, teaches on your own screen when a strategy in your plan needs them. CoraVision reads your account and never uploads, builds or changes an audience itself, and your customer list never passes through CoraVision.
Questions
Is uploading my customer list to Meta allowed?
Yes, with a privacy policy that says you may share customer details with advertising platforms, which most Australian policies written since 2018 include. Meta hashes the list in your browser before it is sent, so Meta receives scrambled values and matches them against its own, and it does not see the names of people it cannot match.
Why does my list of 2,000 customers become an audience of 900?
Meta can only match people whose email or phone number is on a Facebook or Instagram account. A match rate of 40 to 60 percent is ordinary. The unmatched ones are not lost; they are simply not reachable through Meta.
What is the difference between a custom audience and a saved audience?
A custom audience is made of people you know. A saved audience is targeting you set up from Meta's own options, such as women aged 30 to 55 within 20 km of Geelong who follow gardening pages, kept so you can reuse it.