Create text field in magento 2 store for custom lengths.

详细信息

We need to have a "Length" text input field on some of our product pages where the customer can type in the custom length they need for some of our custom cut products like fabric. The products are priced based on the linear footage and have a minimum length. We just need that text field to calculate the price based on the length while still having the "quantity" box on the page. Thanks!