a guide to royal mail size formats
a letter is... a letter!
The Royal Mail definitions are very precise.
To be classed as a 'Letter', an item must be under 100gm in weight, no larger than 24 x 16.5 cm and less than 5mm in thickness.
when does it become a large letter?
The next step up, with a maximum size of 35.3 x 25cm and up to 2.5cm, or 1 inch, thick is the 'Large Letter' format.
A Large Letter can weigh as much as 750gm and might contain things like A4 documents, cased DVDs or magazines.
just how large can a parcel be?
Anything up to 2Kg and 45 x 35 x 16cm is classed as a 'Small Parcel' and can be carried by standard Royal Mail post, just like the two letter formats.
You can, however, use your mailbox for items up to 20Kg in weight and as large as 61 x 46 x 46cm (the Royal Mail's 'Medium Parcel' limits) at no extra charge... but they will have to be forwarded by private courier, especially to addresses abroad.