Mailchimp's import file size limit is 200 MB for CSV and tab-delimited TXT files and 50 MB for Excel workbooks (.xlsx). Larger lists need splitting into smaller files and importing one at a time. Very large files, around a million rows, can still time out even when they're under the size cap.
Moving a big list into Mailchimp usually goes wrong in one of three places: the file's too big, the file's the wrong type, or a column breaks a field rule. Here's each limit, and what to do before you upload.
File size and type limits
| Item | Limit | Applies to |
|---|---|---|
| CSV or TXT upload | 200 MB | Contact import file |
| Excel workbook (.xlsx) upload | 50 MB | Contact import file |
| Legacy .xls, ACT! and .vcf | Not supported | Contact import file |
The gap between the two caps is the thing to notice. An .xlsx file gets a quarter of the room a CSV gets, so if your export's close to 50 MB, save it as CSV first.
Field rules inside the file
| Item | Limit | Applies to |
|---|---|---|
| Text field | 255 bytes | Each text column; longer text is clipped |
| Address line | Fewer than 45 characters | Each line of the address field |
| Zip code field | Five digits | Zip code column |
| Opt-in or confirm date | No more than 72 hours in the future | OPTIN_TIME and CONFIRM_TIME |
| Statuses per import | 1 | Email contact status, such as subscribed or unsubscribed |
The only required fields are the email address for email contacts and the SMS phone number for SMS contacts. Columns you don't match to a field aren't imported, so check the matching screen before you confirm.
When the file's too big, or too long
If the file's over the cap, Mailchimp says to split it into smaller files and import them one at a time. Size isn't the only wall, though. Mailchimp Help's troubleshooting page warns that very large contact counts, on the order of a million rows, can still time out or fail even when the file is under the size cap. Saving as CSV and splitting the file is the dependable route for big lists.
Duplicates and statuses
If an email address appears more than once in your file, it's imported once and updated with the later rows, so your contact count rises by one, not two. That's helpful, but it means the last row wins: if a later row has an older first name, that's what you'll end up with.
Because you can only import one email status at a time, split your file by status before you start. Import subscribed contacts in one pass, and unsubscribed contacts in another, so nobody ends up with the wrong status.
A pre-upload checklist
- Save the file as CSV, unless it's comfortably under 50 MB as .xlsx.
- Split very large lists into several smaller files.
- Separate rows by email status.
- Trim text fields to 255 bytes and address lines to fewer than 45 characters.
- Check OPTIN_TIME and CONFIRM_TIME dates aren't more than 72 hours in the future.
- Remove columns you don't need, since unmatched ones are skipped anyway.
A clean list imports faster and gives you better data afterwards. My CRM data clean-up guide walks through tidying contact data before a move.
Importing from connected apps instead
You don't always need a file. Mailchimp can import contacts from connected apps: Zapier, Salesforce, WooCommerce, QuickBooks Online, Squarespace Commerce and Shopify. If your contacts already live in one of those, a connection avoids the size limits altogether.
How HubSpot's import limits compare
HubSpot allows import files, as of Nov 2026, up to 20MB with its free tools and up to 512 MB on Smart CRM or Starter, Professional or Enterprise subscriptions, with separate daily file and row limits. If you're weighing up email platforms, my MailerLite and Mailchimp comparison is a useful read.
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My advice for a big Mailchimp import
Export as CSV, split the list into a few files well under the cap, and import one status at a time. Run a small file first to check the column matching, then do the rest. If you're moving from a connected app such as Shopify or Salesforce, use the connection instead and skip the file limits.
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Frequently asked questions
What is the maximum import file size in Mailchimp?
200 MB for CSV and TXT, and 50 MB for .xlsx.
What if my list is bigger?
Split it into smaller files and import them one at a time.
Which file types work?
CSV, tab-delimited TXT and .xlsx. Legacy .xls and .vcf don't.
Will duplicates inflate my count?
No. A duplicate email is imported once and updated.
Why did my big file still fail?
Files with about a million rows can time out even under the cap.
