What Are the Dimensions of a C5 Envelope?
C5 envelope measurements, what fits inside, and postage implications.
C5 dimensions
Quick answer
A C5 envelope measures 229mm x 162mm. It fits A5 paper flat or A4 paper folded once in half. C5 is the most popular envelope size for sending folded A4 documents, invoices, and greeting cards. It qualifies as a large letter with Royal Mail, so postage starts at 93p second class or £1.19 first class.
What fits inside
A C5 envelope is designed to hold A5 paper (half the size of A4) without folding. Since most business documents are A4, folding an A4 sheet in half once creates an A5-sized document that slides perfectly into a C5 envelope. This makes C5 the standard choice for invoices, letters, brochures, and greeting cards.
One fold turns an A4 sheet into A5, which is the exact size a C5 is designed for.
Standard A5 greeting cards (roughly 148mm x 210mm) fit comfortably inside a C5 envelope.
C4 (324mm x 229mm) fits A4 flat without folding. C5 is smaller and requires A4 to be folded.
Need other envelope sizes? Check C6 envelope dimensions or DL envelope sizes.
Postage for C5 envelopes
A C5 envelope exceeds the standard letter size limits (240mm x 165mm), so it is classified as a large letter by Royal Mail. This means large letter stamp rates apply: 93p second class or £1.19 first class for items up to 100g.
Where to buy C5 envelopes
C5 envelopes are widely available from stationery shops, office supply stores, supermarkets, and online retailers. They come in plain white, manilla, windowed, and padded versions.
C5 envelopes in bulk
Plain and windowed C5 envelopes at trade prices for businesses and regular posters.
Browse C5 envelopesFrequently asked questions
229mm x 162mm (approximately 9 x 6.4 inches).
A5 paper fits flat. A4 paper fits when folded in half once.
Yes, C5 exceeds Royal Mail standard letter dimensions, so it is classed as a large letter.
Large letter rates apply: 93p second class or £1.19 first class for items up to 100g.
C5 (229x162mm) fits A4 folded in half. C4 (324x229mm) fits A4 flat without folding.
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