If you are attaching files to Gmail from your computer to send the file, then you can only attach files up to 25 MB in size. If you insert a file using Google Drive, then you can send a file up to 15 GB. If you are a paid member, then you can send a file up to 1 TB. By using Insert File feature, you can keep control over who sees your files. To learn how to insert files using Google Drive in Gmail on iOS, check out the steps below.