The Royal Mail's revised pricing system for mail impacts on the way mail should be prepared for posting and on the cost of sending mail.
Mail is not rated just in terms of 1st and 2nd class and on the basis of its weight. Instead the rate is influenced by the length, width and thickness of the mail piece. So for example it is cheaper to fold a piece of mail into A5 size, so that it can be classed as a Letter rather than have it in an A4 envelope, in which case it is classed as a Large Letter and postage costs are higher.
The key principal of this revised system is that smaller, lighter items cost less to send than larger, heavier ones.
For more details on this please visit the Royal Mail website by clicking here.