Uni CPO WooCommerce Options and Price Calculation Formulas plugin gives a possibility to add custom (extra) options to you WooCommerce based products. Having custom options are vital for some products, especially those which depend on customer-defined values/customization choices. Uni CPO plugin can help you to create a price quoting calculator for your product and a possibility to order the product with the quoted configuration instantly.
The video version is available here: https://www.youtube.com/watch?v=dX7-T4gVJ_I
The free version of the plugin is available here: https://wordpress.org/plugins/uni-woo-custom-product-options/ So, go and grab it and install it along with WooCommerce. Now create a product and set its price to smth. Actually, anything, even '1'. This is needed so WC will not treat the product as free. That's all you need to begin product configuration.
Uni CPO has a quite powerful visual form builder. However, it is very easy to use and intuitive. So, activate the builder mode. Add a row by dragging and dropping a module with such a name from the builder panel. Do the same for a column. Now this is the time for custom options. Add Text Input option (again, by dragging and dropping it from the builder panel). Hover it and click on the cogs icon - option's settings modal window will be opened. Define option's slug and other settings such as make it required, step value, default value etc. Save the option.
Create a copy of the whole column - this action leads to duplicating both the column and the option. This is a faster way to add a similar option. Repeat option's configuration but choose a different slug name and save it then.
Now you have two custom options - width and height. Save the builder content by clicking "Save" button on the builder panel. Now open "Formula and conditional logic" modal window and define your price calculation formula. It is as is as writing an arbitrary maths formula. Save it.
Click on "Product general settings" icon on the builder panel and open the modal window with product-specific general options. Enable two first settings here. These are "displaying custom options" and "enable product price calculation". Save the settings.
That's all! Your product has two custom extra options - width and height - and price calculation based on the values of these options. Easy, huh? :)
Also, please, check the pro version of the plugin: https://builderius.io/cpo/ It has a lot more features, tons of features!