Can inventory items automaticaly get multiplied to produce final quantity of product

I have a flex printing business, and in that i have to multiply product size to get final quantity of product, for example if i have sold a 12*10 size flex the total size would be the quantity, can i get or add any feature in sales inventory items from which it automatically multiplies the quantity out for me or i just have to enter the size to get the final quantity and price?

I don’t really understand this. If you are selling quantity of 12*10, you want to enter in invoice literally 12*10 and have quantity on hand reduced by 120?

Why not just enter 120 in the first place?

actualy sir this was just an example! there are much variable sizes n in large quantity each time I had to use calculator first then I had to put tht value in software