How should I write about salary on cover letter when I don't know a range at all?

I think it's perfectly OK to avoid answering requests to disclose your salary conditions. I can almost guarantee that if you're a good candidate for the position, they won't decline to interview you because you didn't specify a salary requirement or range. If they subsequently ask you about it, have enough confidence to say to a recruiter or hiring manager, "Let's talk about my compensation after we determine whether this employment relationship will be mutually beneficial for both of us." Let the merits of your candidacy speak for themselves. If they want to give you a job offer, let them "make the first move" regarding salary. If they think you're desperate for a job, they'll low-ball you. If they think you're talented and that you could easily work elsewhere, they'll offer you a competitive salary or even a salary above the market wage rate. If you get suckered into providing them with your salary expectation, and your expectation is low, they'll low-ball you regardless of how good you are. If your expectation is high, they won't even offer you the job if your candidacy doesn't perform up to those high expectations. Giving a prospective employer your salary expectation is a lose-lose for you, so that's why I say don't do it. If you feel like you MUST give a salary expectation despite my advice, then never give a range because the employer will always go straight to the low end of your range. Try http://www.glassdoor.com for a better sense of what the typical salary is for that position, and ask for the high end of that. Keep in mind that job seekers are not powerless. Employers need good employees just as badly as employees need jobs, so don't assume that you always have to jump through every hoop that a prospective employer wants you to jump through. Have enough confidence in yourself to politely decline to do something that puts you at a distinct disadvantage.

Try going online and searcing for: "Salary Calculator". If you are applying for a field you have never worked in, expect a lower salary. If you have relevant experience, expect a higher salary. I'd take what you are currently making hourl and multiply by 1.35 and calculate the new annual salary. This number is negotiable and they know that. They just want a ball-park. If you are requesting more than you are worth they will wonder why. They may also screen based on salary, so keep that in mind and DON'T shoot for the stars.