Donald Miller said:
As an alternative to what you question, I prepared a CD of my work.
Not do discourage anyone from this practice as it is a good way to show work to those that request to see it. But sending CDs on "cold calls"... unsolicited inquiries without some sort of printed imagery can be a waste of time and money. I am affiliated with several galleries and can tell you without a doubt that most just throw them away. There are a million wannabe photographers out there and these galleries get upwards of 5-10 solicitations a day. Most are much of the same old, same old and don't even get a second look. Cards, prints, etc at least get a quick look before they go in the garbage. Cds go straight in the circular file. They are not interested in taking the time to boot them up on the machine. In the very rare case that they see something printed that they like, they
might take the time to look at your CD.
Also... never send anything to a gallery unsolicited that you want back... even if you enclose return postage. Except in the rare case, or if you have called ahead of time and arranged return, you will never see your material again.
To answer Pete's original question, make them the size that you think they look best. And remember the saying "your portfolio is only as strong as its weakest image". In most cases it will be the only chance you get with a particular dealer. If they look at you once and are not interested, there won't be a second opportunity.
Good luck!!
Bill