There are many factors that determine a patent attorneys salary (or patent agent). The major factors include your degree level, your experience, and where you seek employment. Let's start with your degree level.
Since the major criteria for entering a career in patent law is your technical background, there is a wide range in pay depending on your exact area of study and the degree you possess. For instance, there are many patent attorneys and agents in the field of biotechnology. Depending on the job market, those with backgrounds in biotech may earn higher salaries than those with engineering backgrounds. In addition, you might expect to command a higher salary if you have a Ph.D. or a Master's degree versus merely a Bachelor's degree.
Your experience will play a big part in determining your salary as well. Although experience in science and engineering may help, it will be more beneficial to have experience writing and prosecuting patents. For that reason you can expect to command a higher salary the longer you have worked in the field of patent law. Patent attorneys or agents just starting out will typically earn the lower salaries.
Where you seek employment will also play a role in your salary. This includes what type of setting you plan to work in (law firm, government, corporation, technology transfer office, etc.). Typically, law firms pay the most whereas working in a university technology transfer office will likely pay the least). In addition, the geographic location of your next position will also likely factor into your pay scale as well.