You know how to work out the price of sending a letter. After all, you've been doing it the same way for years.
Previously the price of a stamp depended purely on the weight of the letter or packet. And as size wasn't an issue there was only one price table you needed to look at to work out the price.
So now you need to determine the size of your item first to use the correct price table.
Locally there is no increase for all standard sized letters (known as DL and C5 envelopes) under 100g and less than 5mm thick.
In other cases savings can be made. For example, if you send an unfolded letter in the standard sized envelope (known as a C4 envelope) it will cost 48p within the Bailiwick. If folded in half and sent in a C5 envelope the same letter costs just 36p to send.