Total weight in order mail.

Hello,
Opencart 2.3.0.2, default theme. Flat rate shipping and free shipping active.

I have searched the forum, but couldnt find any good information for what I am looking for.
What I need is that total wait is shown in the mail that goes to the admin when new order is placed. Nice if that can be in mail to customer also. Which files are responsible for generating these mail when an order is placed.

Maybe any of you know of a good extension that can do this.

catalog/model/checkout/order.php
catalog/view/theme/<your_theme>/template/mail/order.tpl

Thank You. I think I can work it out from here.