Dimensions for Behringer products are listed in the unit's specifications which can be found in the Quick Start Guide or Manual on the website. For example in the case of the Xenyx QX2222USB you would go to the product's page and click on the 'Downloads' tab:
Scroll down the page and under the heading 'Documentation' you will see links to the unit's Quick Start Guide and Manual:
You can go into either of these documents and head to the specifications. In manuals the page of the specifications will be shown in the Table of Contents, in quick start guides they are toward the end of the document. You will see the size of the product both inches and mm and weight in both Kg and lbs as shown below. For some products approximate values will be given.