Royal Mail Letter Sizes - Postage Costs For Envelopes
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 C4 Envelopes