Collection: C3 Envelopes (324 x 458 mm)

C3 envelopes measure 324 x 458mm and are designed to hold A3 documents unfolded — the largest standard C-size envelope format. With over 15 products, the C3 range is a specialist format used for architectural drawings, A3 prints, large brochures, legal documents and event materials that must not be folded.

What Fits in a C3 Envelope?

A C3 envelope (324 x 458mm) holds: A3 paper unfolded (297 x 420mm), large architectural drawings, A3 brochures and magazines, oversized event invitations (weddings, galas, company dinners), prints and posters up to A3, and multi-sheet document packs. It is the correct format wherever A2 or A3 material must be sent flat.

Benefits of C3 Envelopes (324 x 458mm)

• A3 capacity — holds A3 paper unfolded (297 x 420mm) — no folding required.
• Specialist format — the largest standard C-size, suited to architectural, design and large-format document dispatch.
• Paper weights 70–350gsm — appropriate for large-format professional document mailing.
• Royal Mail compatible — posted as small parcel or medium parcel depending on contents weight.

Frequently Asked Questions

What fits in a C3 envelope?
A C3 envelope (324 x 458mm) holds A3 paper unfolded (297 x 420mm). Common uses include architectural plans, large print artwork, A3 brochures, legal document bundles, event programmes (wedding, conference, gala) and any oversized flat item that cannot be folded.

What Royal Mail category are C3 envelopes?
C3 envelopes are too large for Large Letter format (max 353 x 250mm). They fall into Small Parcel (max 450 x 350 x 160mm, up to 2kg) or Medium Parcel depending on packed dimensions and weight. Always weigh and measure the packed item before assigning a postage rate — C3 envelopes are specialist formats typically posted at small parcel rates.

Are C3 envelopes the same as A3 envelopes?
C3 envelopes are designed to hold A3 paper unfolded. The envelope (324 x 458mm) is larger than A3 paper (297 x 420mm) to allow the document to fit inside with clearance. When someone refers to an 'A3 envelope' they typically mean a C3 envelope — the C-size convention adds approximately 27mm in each dimension over the equivalent A-size paper.