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Our guide to selecting the best envelope

'C' envelopes are slightly larger than their 'A' paper counterpart. 

C4 envelopes therefore hold an A4 sheet unfolded, or a thin brochure or catalogue.

C5 envelopes hold an A4 sheet folded in half.

DL envelopes hold an A4 sheet folded into thirds. They are a good size for cheques and standard compliments slips.

C6 envelopes hold an A4 sheet folded into quarters.

Royal Mail classes anything under 100g and 240mm x 165mm x 5mm as a Letter, while anything above this and under 750g and 353mm x 250mm x 25mm is a Large Letter.

As you might expect, Large Letters are subject to higher fees, so you should use smaller envelopes wherever possible. You can find the envelopes and their sizes categorised according to the Royal Mail pricing system in the table below. Remember that you must also take into account the thickness when posting:

Royal Mail category

Envelope Size

Letter DL 220mm x 110mm

C10 40mm x 28mm

C9 57mm x 40mm

C8 81mm x 57mm

C7 114mm x 81mm

C6 162mm x 114mm

C5 229mm x 162mm

Large Letter

C4 324mm x 229mm


Just as with paper, envelopes are measured in GSM (grams per square metre). This weight is an indicator of thickness. Our Premium standard envelopes are around 100GSM, but if you need something that withstands higher levels of wear-and-tear and looks more professional, around 120GSM is recommended.

Envelopes come in a huge variety of colours. You will even find envelopes made from recycled materials.

Specialist envelopes

There are a number of specialist envelopes that will help you more effectively with most projects.

FSC Mix Credit

FSC stands for the Forest Stewardship Council. All our envelopes are produced using a mix of material from sustainable FSC certified sources. FSC standards protects forests through preventing practices such as illegal logging, and civil rights violations.