How can I tell if I have dense breast tissue?

Dense/fibrous tissue is usually a classification (or even a comment) that a doctor would make. It's hard to describe but it could mean anything from thick or full to bumpy/lumpy breasts.

This is probably a terrible comparison, but if you feel your cheek it should be soft, easy to compress and 'smooth' wherease dense tissue isn't.

Essentially having dense tissue makes feeling for unnatural lumps more difficult (or mammogram readings harder to interpret).

Basically go talk to your doc :)

It isn’t something you can tell on your own. It has nothing to do with how small or large or smooth or bumpy your breasts are. It can only be seen radiologically. On mammograms dense tissue is light and so are tumors, so they blend right in making them difficult or impossible to see.