Currently, there isn't a direct way of adding another column for the unit of measure on your forms. Don't get worked up, I got alternative steps for you.
To accomplish your goal, we can utilize the Description column on the form to attach the unit of measure. I'll be delighted to guide you on how:
In your QBO account, proceed to the Sales menu.
Select All Sales.
Choose the form you want to add the unit of measure.
Click the Description column and enter the U/M.
Once done, select Save and close.
Another way is by using the Description field on the Product/Services information page if you want to enter specific measurements for your items.
We also offer ready-made articles you can access to help manage and personalize your sales forms: