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Royal Mail Letter Sizes

Here you will find detailed information including sizes and costs for sending standard letters and large letters with Royal Mail.

Royal Mail Size & Weight Guide For Letters

Max Weight Max Length Max Width Max Thickness
Letter 100g 24cm 16.5cm 5mm
Large Letter 750g 35.3cm 25cm 2.5cm


Ideal for mailing greeting cards, regular letters and postcards, the maximum size that would fall under a 'letter' is 165 mm x 240 mm. We would recommend using an envelope no larger than C5 to fit these restrictions comfortably and avoid any excess costs. The envelope and contents must also weigh under 100g.

Recommended envelope sizes

Cost for sending a letter

Service Price
1st Class 85p
2nd Class 66p

Large Letters

For mailing contents such as A4 sized documents, DVDs, certificates, large greeting cards and magazines you would need to send as a large letter. The maximum size is 250 mm x 353 mm and and a maximum weight of 750g so a C4 envelope is a good choice.

Recommended envelope sizes for a large letter

Cost for sending a large letter

Weight 1st Class 2nd Class
up to 100g £1.29 96p
101g to 250g £1.83 £1.53
251g to 500g £2.39 £1.99
501g to 750g 3.30 £2.70