Adding sold volume to sales fact table

Hi!

I´ve a fact table containg order-lines.
Something like this:

**OrderLineKey
*OrderKey
*TimeKey
*ProductKey
Quantity
SalesAmount

I want to add the measure sold volume. Also quantity*volume_of_product. Should I add the column "SalesVolume" to the same fact table or should I add product-volume to the product-dimenssion and make some kind of calculated measure?

Best regards