Answer:
No. At least not in terms of number of words or size of type.

That's because the message that works in your headline will vary depending on the nature of your offer, the promotional format you've chosen, and how much room you have to present supporting claims. There are some accepted rules of thumb, however, that have been proven time and time again over the years. Here are a few general guidelines that will get you on your way.

1. Use a short "grabber" headline that piques curiosity or arouses emotion. For example, you almost have to read further when you see "Bill Gates reveals his biggest boo-boo" at the top of the page.

2. Use the name of your product or service in your headline if at all possible.

3. Make a daring promise in your headline (e.g., Spot-free windows in only 30 seconds).

4. Imply that a bargain exists through acceptance of your offer.

5. State the problem and reveal a solution (in the form of your offer). Boring, yes, but it will serve to cut through a lot of the hype battling for your reader's attention.