How to split a large CSV file into smaller files that keep the header

Full system exports, customer databases and transaction histories grow fast. At some point the CSV file becomes too big for what you need to do with it, and the way out is to split it into parts.

When a CSV needs to be split

• Excel limit: a sheet holds at most 1,048,576 rows. With more than that, Excel opens only the beginning and warns that the file was not loaded completely; the rest simply does not appear.
• Import limits: online stores, email platforms, CRMs and business systems often accept a maximum number of rows or a maximum size per upload.
• Email attachments: services such as Gmail limit attachments to 25 MB.
• Team work: sharing a large list among several people, each with their own part.

Why not cut it by hand

Opening the file in a text editor and cutting out chunks looks simple, but it is easy to cut a row in half, forget the header in the later parts or break the character encoding when saving. Command-line tools such as the Linux split command divide by lines, but they do not repeat the header either, so every part after the first is imported without column names.

How to split with the Split CSV tool

Split CSV splits files in two ways:

• By rows per file: you set how many rows each part will have, for example 1,000 or 50,000, according to the destination limit.
• By number of files: you say how many parts you want, and the rows are spread evenly.

Before creating them, it shows how many parts you will get. With the repeat header option on, every part starts with the same title row as the original and can be opened or imported on its own. The original delimiter is kept and values are not changed: leading zeros and dates stay exactly as they were. The parts are numbered in sequence and delivered in a single ZIP file, in UTF-8.

Tips for choosing the part size

Start from the destination limit and leave some margin: if the platform accepts up to 10,000 rows, use 9,500. If the limit is in megabytes, divide the file size by the limit and use a slightly larger number of parts. For opening in Excel, anything below a million rows per part works, but smaller parts open faster.

Once the parts have been processed, if you need to bring everything back together, Merge CSV does the reverse, with the header only once.

Frequently asked questions