Sorting mails by size is a feature which is not available in Gmail by default. This is possible only by a third party application. Go to www.findbigmail.com – which is website that helps you sort your mails by size.
Steps are very simple, just enter your Gmail id and click the button. This will access your Gmail account so you will have to give the grant access. They say it is secured and they don’t store our password. They just access your account and sort the mails based on the size. I would say not to try this If you feel it is not safe. But I have tried this and it works and nothing to worry about the personal mails. I have changed the password after doing this to be on the safer side.
Coming back, when you are done by providing the Gmail id it starts sorting your mails by size. When the progressing starts it gives out a message saying ‘ this may take few minutes depending on your mailbox size.’ and when it completes it sends a mail to your Gmail account.When you now see your account you could see some folders based on the size of your mails as shown in the screenshot below. The mail which was sent by findbigmail shows the scan result.