Font Size: The traditional font size for a professional letter is 12. The font should be Times New Roman or Arial. However, if you are using letterhead, the letterhead may be in different font size and style. Font Style: There is no need to use different styles within a professional letter. Use a uniform font (book print font such as Times New Roman or Arial) and avoid underlining, italicizing, or bolding. However, if you are using letterhead, the letterhead may be in a different font style.
Business Letter Writing Guidelines. Here are guidelines for writing a business letter, so all your correspondence makes the best impression. Margins: Business letter margins should be about 1" all around. This gives your professional letter an uncluttered look. You should align your text to the left; this is how most documents are aligned, so it will make your letter readable. Letter Spacing: Leaving space in your letter creates a clear, uncluttered and easy to read look that the reader will appreciate. Your letter should be in block format: the entire letter should be aligned to the left and single_spaced except for a double space between paragraphs.