How do you prepare a customer list for a custom audience?
Put your customers' details into a CSV or TXT file with at least 1,000 customers and at least one main identifier, such as email or phone, each type in its own correctly formatted column. Meta says to give phone numbers a country code and put the country in its own column. The list is hashed before matching.
Meta matches identifiers such as emails and phone numbers to its profiles, so your column layout and the identifiers you include affect how much of the list can match. This page covers the file. For the upload clicks, see how to create a custom audience.
What must a customer list file contain?
Meta’s formatting page says a customer list should:
- Be a CSV or TXT file
- Include at least 1,000 customers
- Include at least one main identifier
- Use the correct column formatting for each identifier type
Meta says to include as much information as possible for the best match rates. Figures are as checked on 2 Oct 2026.
Which identifiers can you include?
Meta says you must add at least one main identifier and recommends more than one.
| Identifier | Column header | Meta’s rule |
|---|---|---|
email |
Up to 3 separate columns, one address per cell | |
| Phone number | phone |
Country code required, up to 3 columns, with or without punctuation |
| Mobile advertiser ID | madid |
Android advertising ID (AAID) or Apple IDFA |
| Facebook app user ID | appuid |
Numerical ID tied to your Facebook app |
| Facebook Page user ID | pageuid |
Numerical ID of someone who interacted with your Page |
Meta also accepts optional identifiers to use alongside a main one: fn, ln, ct, st, country (an ISO two-letter code such as us or gb), zip, dob (18 date formats), doby (four-digit year), gen (an initial) and age (a number).
A value column must hold numbers only, with no currency characters. Meta says it lets you create a value-based lookalike audience later.
How do you lay out the file?
- Put each identifier type in its own column, with first names and last names in two columns instead of one full-name column.
- Use Meta’s column headers. If you use your own, map each one to its identifier type before you upload.
- Add the country code to every phone number, even if all your customers are in one country.
- Add a
countrycolumn, even if every row is from the same country. - Check the mapping screen: a check icon means the identifiers are ready to hash, and an exclamation point means one was skipped or needs updating.
Meta calls the phone and country rules its two most important tips, and says the country column helps because it matches on a global scale. It says fixing mapping warnings before you upload improves your chance of a better match rate.
What does hashing do to your list?
Meta says hashing is a cryptographic method that turns your identifiers into randomized code and cannot be reversed. Its About customer lists page says this is done on your own machine, before the list is sent. Its create page says the data is hashed before matching, which may take a few minutes depending on list size.
What information is not allowed?
Meta says a customer list audience cannot be named, include or be based on prohibited information, and you need the rights and a lawful basis to use what you upload. Its examples, which it says are not exhaustive:
- Data about people who opted out of use in targeting audiences, and about children under 13
- Social security numbers, passwords, GPS data, access tokens and public services identifiers
- Financial account or status information, and physical or mental health information
Under GDPR, Meta says you act as the data controller for any list you upload.
What is an only exclusions customer list?
When you add a list, you choose whether the audience is for inclusions or exclusions, or only exclusions. Meta says only exclusions suits people you always need to exclude, such as people who opted out of marketing.
Two limits apply. You cannot change the choice later, and you cannot build a lookalike audience from it. Under include these custom audiences it appears grayed out, so nobody on the ad account can use it there. See how audience exclusions work.
How do you check the result?
In Audiences, add the match score column. Meta says it is a score out of ten for your last successful upload, in steps of 0.5, calculated by dividing matched rows by uploaded rows. Adding more emails, phone numbers and device IDs can improve it. If no score shows, you may need to update the list. Outdated means the list hasn’t been updated in over 30 days. If the audience stays empty, read why a custom audience is not populating.
FAQ
Can I upload a list with fewer than 1,000 customers?
Meta’s formatting page lists at least 1,000 customers among what a customer list should include. It does not say what happens below that number, so check the audience status after you upload.
Do I hash the file myself before uploading?
Meta’s formatting guidance covers column layout, not how to hash. Its About customer lists page says hashing is done on your own machine before the list is sent; its create page says the data is hashed before matching.
Can I change the list after I upload it?
Yes. Meta says you can add, remove or replace customers at any time. Changes also update the ad sets and lookalikes that use it without resetting learning, and may take a few hours.
Sources
- Customer list formatting guidelines for custom audiences (Meta, checked 2 Oct 2026)
- Prepare your data for a customer list custom audience (Meta, checked 2 Oct 2026)
- Create a customer list custom audience (Meta, checked 2 Oct 2026)
- About customer lists (Meta, checked 2 Oct 2026)
- Edit a customer list custom audience (Meta, checked 2 Oct 2026)
Drafted with AI and checked claim by claim against the pages linked under Sources. Found a mistake? Tell us via the corrections policy.