Custom line item total calculation I have looked for the solution for weeks, but I have not found any. It must be very trivial that I missed.

I'm adding a line item field in addition of the default unit price and quantity called "length" in the cart view and Order. I would like to get the new calculated line item total = price * quantity * length.

Solutions that I have found so far change the line item unit price, which is not desirable.

How can I do this?
The line-item unit price is used throughout commerce and the total order amount is based on the line-item total value (quantity * unit price). There is no way to circumvent this behavior.

Better would be to add another price field to the line-item Price per length-unit. Hide the default price field and calculate the sales price as you've found in other answers.

Basically this is a pricing rule in Store &gt; Configuration &gt; product pricing rules where you add the event Set the unit price to a specific amount to a calculated value.