How can I measure texture memory used?

How can I measure how much texture memory I am using? Is there a better option then calculating a best guess based on texture sizes?

Its the size of your XNB.

The size of the XNB is a good guide, as the data from the XNB is loaded straight into the texture. There is a little overhead from the XNB header, but this is relatively small compared to the memory use of the texture data.