Welcome to the Community. I can share some information about the products and services in QuickBooks Online.
Currently, a specific field for the product dimension is unavailable. As a workaround, you can add this type of information together with the item name or by using the Description field.
Here's how:
On the left navigation bar, click Sales.
Go to the Products and Services tab.
Select New to create a new item or Edit to update existing information.
Add the item dimension in the Name or Description field.
Hit Save and close.
I can see how beneficial this feature to you. We'll continue to improve QuickBooks, and this preference might be available in the future.
As we assess this, I suggest you visit our QuickBooks Blog to stay updated with all the changes in the product.