The biggest shake-up in postal pricing since the introduction of the Penny Black comes into force on Monday 21 August.
The cost of posting a letter will depend on size and thickness as well as weight. Charges will be based on three size formats – letter, large letter or packet.
Sending a standard-sized letter weighing up to 100g will still cost 32p. But an A4 envelope weighing up to 100g and up to the thickness of a cigarette packet will be classed as a large letter, and will cost 44p.
To publicise the changes the Royal Mail’s targeted every UK household as part of a £10 million information drive. Homes were due to get a paper template to help them size up letter before posting.
Royal Mail says that, under the new pricing scheme, compact, heavy items such as books will be cheaper to send, while light but bulky items, such as a poster tube, will cost more.