A simple rule of thumb for copy length

When deciding whether you need long copy or short, whether in a landing page, e-mail, or sales letter, follow this simple rule: short copy for generating leads, longer copy for generating orders.

"As a general proposition, an ad in which you are seeking only inquiries should be short, merely leading the reader down to the free booklet and the coupon," writes copywriter Robert Collier, "whereas an ad in which you are attempting to make the actual sale should be long enough to tell all about your offer.

"Some authorities will tell you to write only short, crisp ads, with plenty of white space—others to crowd in every word you can get. Both are wrong. There is no hard and fast rule as to how long an ad should be, except that it should be long enough to tell your story, but short enough to hold your reader's interest."

Source: Collier, Robert, "How to Make Money at Home in Spare Time by Mail", p. 154