Is a 9mm nodule worst than 1.2 cm nodule?

Depends: A 9 mm nodule is a lot smaller than a 1.2 cm. nodule. But it depends on what is causing the nodule and where it is. A small cancerous nodule would be worse than a large noncancerous nodule, generally speaking. So give more details please. Location of either of the nodules is important to know, too, when trying to answer your question.

Nodules: Usually smaller is better. So in this regard, 9mm (0.9cm) is better than 12mm (1.2cm). However, if we're talking about cancer then another important factor is how aggressive the cancer cells are, i.e., how fast they grow/spread. And this you can't tell by size alone but need to look at cells under a microscope and also evaluate for any other nodules or masses.

No: 9mm is smaller than 1.2cm. 1.2cm is 12mm. Both are smaller than a half inch.