Royal Mail’s Pricing in Proportion (PiP) Initiative

While Royal Mail's current system is based only on the weight of your items, the new PiP initiative will be based on both the size and weight of your item. There will be three main size formats - Letter, Large Letter and Packet:
 

Letters Letter covers items including most postcards, bills, statements and most greetings cards. The price for posting these items won't change - in fact you can still use your existing stamps on Letters. Length:240mm max Width:165mm max Thickness:5mm max Weight:100g max
Large Letters This covers items such as magazines, CDs or in some DVD's in cases (depending on their thickness), and A4 envelopes. The price of a Large Letter stamp starts at 44p Length:353mm max Width:250mm max Thickness:25mm max Weight:750g max
Packets This covers anything longer OR, thicker OR wider than a large letter - so packets include items such as VHS cassettes, books, prints and posters in cylindrical packaging. You'll need to weigh these, just as you do now, to see the new cost prior to sending. Length:over 353mm OR Width:over 250mm OR Thickness:over 25mm OR Weight:over 750g

Information to help you work out the price and size of the item you are sending along with details of all products affected by the new pricing system like first class stamps, freepost and prepaid products is available from the Royal Mail website and for your convenience we have included these direct links below:

Royal Mail PiP Price Guide
Order a Size Guide
Product Affected by PiP
Frequently Asked Questions

Also See:
C4 Envelope
C5 Envelope
DL Envelope
Board Back Envelopes
Protective Envelope
Padded Bags
 

Source: Royal Mail Group plc