Usually, one paragraph. Identify your recipient. State your purpose in writing this letter. Give some general background information that says why you are a good candidate.
Two to three paragraphs that show your educational background, work experience, and skills that fit the recipient organization's needs. Put your greatest strengths first to emphasize them.
Remember that you are making an argument: you are trying to convince someone to hire you or accept you into their school program. Offer evidence that proves you will be an asset to their organization. Each paragraph should begin with a claim, and then use specific examples from your education or work experience to justify that claim. The introduction was where you talked in general terms why you would be a good candidate; now is the time to get into specifics. Usually, the more specific you can be with numbers and dates, the better. If you can identify specific needs or programs that the recipient organization has and that you can contribute to, do so.
The body of your cover letter should tell a story about yourself and why you would fit the organization to which you are applying, and how you can contribute to it.
Thank the reader for the opportunity to apply. Offer contact information and make a statement that looks forward to joining their organization. Do not beg or plead for acceptance. Be positive and try to make a positive impression.
Adapted from: Johnson-Sheehan, R. (2015). Technical communication today (5th ed.) Pearson.