Make a product, with price based on weight

Hi, so how do i easiest add a product like, let’s just say rice or corn. How do i say like pr. Kg $1. And then you choose how many Kg you want and the it calculates the price, and you can add it to the basket.

I’ve tried with variables, attributes and variations, but it’s really confusing!

Please help someone ??

Thank you

https://www.ads-software.com/plugins/woocommerce/