What size is a small letter royal mail

According to Royal Mail's size and weight guidelines, a small letter is defined as a package that meets the following criteria:

These dimensions and weight limits apply to both domestic and international small letters. If your package exceeds these limits, it will be classified as a large letter or a parcel, which may incur higher postage costs.

Keep in mind that Royal Mail also has specific rules for packaging and labeling small letters, including requirements for addressing, labeling, and packaging materials. It's always a good idea to check the Royal Mail website or consult with a postal representative for the most up-to-date information on sending small letters.