how can I change unit measurement and unit pricing for goods when I purchase and sell lets say selling beef by pricing / pound , but you really selling by the box .

You can change the unit pricing by adjusting the price/rate, Biao. Here are the steps:

1. From the left panel, select the Sales menu.
2. Choose Products and Services.
3. In the Products and Services tab, click the item you need to modify and hit the Edit button.
4. Scroll to the Sales section and enter your modifications in the Price/rate box.
5. Then, click Save.

QuickBooks Online does not have the functionality to edit or add unit measurements, regardless of whether items are sold individually or by box. Thus, I suggest submitting your feedback to our product engineers to consider adding this in future updates.

Here's a reference for creating products and services and other changes you can make: Add product and service items to QuickBooks Online.

Additionally, I'd like to share this helpful article on organizing your products and services into groups: Categorise products and services.

Feel free to reach out if you need further assistance with setting up products and services or if you have any questions in the future.

Good day, @BIAO-WANG 

I updated my response above about your concern, as I missed something and wanted to ensure I provide accurate information.

Let me know if you have any further questions or need assistance. We're here to help.