Should you mail a one-page letter or a two-page letter? Neither. Mail a four-page letter.
I'm talking about donor acquisition letters. The ones you mail to strangers, asking them to send you a gift. The most successful acquisition letters are longer than your typical renewal letter. Here's why.
Renewal letters, by definition, ask current donors to renew their support. So these letters assume that donors understand who you are, what you do, who you help, and why you are a worthy cause that deserves the donor's support.
But a donor acquisition letter usually lacks all of these advantages. It must assume that the reader knows little about your organization and your mandate. Which means an acquisition letter can't simply ask for another gift, since the reader has never given before. An acquisition letter, instead, has to ask for a first-time gift. And that requires more than a simple request for a gift.
Acquisition letters, even though most of them begin "Dear Friend," are written by strangers to strangers. So introductions are in order. Your organization must introduce who you are. You must describe what you do, and who you help, and where you operate, and so on. This takes time, and so it takes words, and so it takes space, more space than one page of a sheet of 8.5 x 11 inch paper.
Another reason that donor and member acquisition letters are often longer than two pages is that you have more objections to overcome. Current donors trust you. Strangers don't. That's why many acquisition letters describe how the organization spends each donated dollar, something you'll rarely see explained in a donor renewal mailing. Commonplace in acquisition packages is a description of the percentage of each dollar spent on programs, administration and fundraising.
Another reason acquisition letters often run to four pages and longer is inertia. Potential donors can think of all sorts of reasons not to support your cause. They are like cars without gas. Or, the stay with the analogy, engines without sparkplugs. Your letter must act as the gas that propels the car forward, the spark that ignites the fuel. That can rarely be accomplished on one page. Even the most compelling causes need more than one page to tell their story and inspire people to act. 
