The size and weight restrictions for MK Mail & Logistics Letter and Packet delivery services are as follows:

UK Sorted and Unsorted Mail

Letters
Minimum size: 140mm x 90 mm
Maximum size: 240mm x 165mm x 5mm (depth)
Maximum weight: 100 grams.

I.e. most cards, postcards and bills

Large Letters
Minimum size: 140mm x 90 mm
Maximum size: 353mm x 250mm x 25mm (depth)
Maximum weight:  750 grams.

I.e. most A4 documents, CD’s and magazines

Packets
Minimum size: 353mm x 250 mm x 25mm (depth)
Maximum size 601mm x 460mm x 460mm (depth)
Maximum weight: 2000 grams.

I.e. gifts, magazines and books

International Letters & Packets

Letters
Minimum size: 140mm x 90 mm
Maximum size: 240mm x 165mm x 5mm (depth)
Maximum weight: 100 grams

Packets
Items:  Maximum length 600mm
Tubes: Maximum length 900mm. Length + 2 x diameter should not be more than 1040mm
Maximum weight 2000 grams