Facebook Custom Audience File Format: Columns, Phone Rules and What Lowers Your Match Rate

A Facebook custom audience file is a CSV with one person per row and Meta's own column names: email, phone, fn, ln, ct, st, zip and country, each normalised to Meta's rules. The values matter as much as the headers: lower-case emails, phones as digits with a country code, names and cities in lower-case letters only. The Facebook custom audience file formatter writes that file from a CRM or lead export. Before you upload it, check the addresses. A closed mailbox can't match an account, and it was never going to lift your audience size.

Format a customer list for Meta →

What Meta's docs say about each column

These rules come from Meta's developer guide on custom audiences, read on 9 November 2026, in our words.

Column	Normalisation rule
email	Trim spaces at the start and end; lower-case
phone	Remove symbols, letters and leading zeros; add the country code if no country is given
fn (first name)	Lower-case, letters a to z, no punctuation
ln (last name)	Lower-case, letters a to z, no punctuation
ct (city)	Lower-case, a to z only, no punctuation, special characters or spaces
st (state)	US: two-character ANSI abbreviation, lower-case. Outside the US: lower-case, no punctuation or spaces
zip	Lower-case, no spaces; US: first five digits only
country	Lower-case ISO 3166-1 two-letter code

Meta's docs also list other keys such as date of birth parts and gender. The formatter doesn't write those. One note in the docs: for first and last names, the table allows UTF-8 special characters, but the text recommends Roman-alphabet translations with no special characters for the best match rate.

Which columns matter most

Email or phone gives the strongest matches. Names, city, state, ZIP and country add context that helps Meta match the rest. Having more columns filled in for each row helps, but a row with only a good email still counts.

Rows with neither a usable email nor a usable phone are of little use, and the formatter leaves them out and counts them so you can see how much of the export was empty.

Hashing: when it's needed

Meta's developer docs say data must be hashed with SHA-256, with the hex output in lower case, for all keys except a few such as external identifiers, app user IDs, page-scoped user IDs and mobile advertiser IDs. They add that you normalise first, hash on your side, and send the hashed values.

That is the rule for the Marketing API. For a file you upload by hand in Ads Manager, we didn't verify Meta's current wording, so read its customer list help page before deciding. In both cases:

• Sending through the API, or giving the list to a partner who uploads it: hash the normalised values with SHA-256. The formatter has a tick box for that, and the email hasher hashes a plain address list.
• Uploading by hand: start from a well-formatted plain CSV and follow what Meta's page says about hashing.

Normalise first, then hash. Hashing [email protected] and [email protected] gives two different results, and only one can match.

The upload itself

In Ads Manager, the route is Audiences, then Create audience, then Custom audience, then Customer list. You upload the CSV, map columns if asked, and name the audience. If the headers are Meta's names, mapping is automatic.

Meta then matches the identifiers against its own data. You don't see who matched, and the audience can take a while to fill, so don't judge it in the first minutes.

What lowers a match rate

Match rate is the share of your rows that Meta could connect to an account. These problems pull it down:

1. Raw phone formats. Numbers written as (415) 555-0132 or +1 415 555 0132 with no consistent country code.
2. Mixed-case or padded emails. Fixed by trimming and lower-casing.
3. Merged name columns. "Jane Doe" in one cell can't fill fn and ln. The formatter splits a single name column into first and last.
4. Dead addresses. Nobody is on the other end. Old newsletter lists and trade-show exports are the worst for this.
5. Addresses the person doesn't use on Facebook. Work emails in a consumer-facing audience, or a shared inbox like info@. You can't fix this with formatting, but phone numbers can help fill the gap.
6. Typos. gmial.com doesn't match anything. Email typo correction shows how to find these.
7. Duplicates. Repeats inflate the file without adding a person. Run remove duplicate emails first.

Custom audience match rate looks at why match rates differ between lists.

A clean process, in order

1. Export the contacts from your CRM or store as CSV or Excel.
2. Verify the emails at /verify. Remove invalid rows. Keep risky ones out of audiences you pay to reach, unless you have no other contact data for those people.
3. Format the file with the formatter: pick a default country for rows without one, check the columns it found, and tick SHA-256 only if you need hashed values.
4. Upload in Ads Manager under Customer list.
5. Wait for the audience to populate, then check its size against your row count to estimate the match.
6. Refresh the audience from time to time. A list you uploaded a year ago has lost people, and gained none.

What to use for what

Goal	Use
Build the audience from a CRM export	Facebook custom audience file formatter
Remove dead emails first	/verify or the email list cleaner
Hash a plain list for a partner	Email hasher
Remove opted-out people before upload	Scrub against your suppression list
Lead ads export with messy columns	Clean Facebook lead ads leads

Limits of the formatter

• Columns are found by header name. Rename an unusual header like "Contact pt." to Email, Phone or Name first.
• It keeps one email and one phone per person; extra address columns aren't merged in.
• It doesn't write date of birth, gender or mobile advertiser IDs.
• Formatting can't make a closed or unused address match an account.

Quick answers

• CSV or Excel? Either can go into the formatter; it writes a CSV.
• Do capital letters matter? Yes. Meta's rules say lower-case for every identifier.
• Should I verify a customer list I already own? Yes, if it is more than a few months old. People change addresses, and a customer list is not immune.

Try it on your own list

Upload a sample at /verify. The first 100 checks are free with a Google sign-in, no card.

Pro, $39 a month: Unlimited email verification.* Never metered, never cut off. See pricing.

*Fair use: the first 100,000 checks a month at full speed, then slower, never cut off.