What size should I choose for a mailed brochure?

For anything you plan to mail, stick with sizes that fit standard envelopes and qualify for regular postage. Letter tri-folds and Half-Letter bi-folds are the reliable choices, and non-standard shapes tend to cost more to send.

The 8.5" x 11" tri-fold is the standard mailing pick because it keeps postage low while leaving plenty of room for your message, offer, and contact details. Avoid square and Tabloid formats for mailing, since they need custom envelopes and push postage higher.