How much clearance should an envelope have?

A minimum of 2-3 mm clearance on each side is recommended so the card slides in and out easily. For thick cards or cards with embellishments, allow 4-5 mm. Too tight and the card will be difficult to insert; too loose and it will slide around.

What are the standard UK envelope sizes?

The most common UK envelope sizes are C6 (114 x 162 mm, fits A6 cards), C5 (162 x 229 mm, fits A5), DL (110 x 220 mm, fits A4 folded in thirds), and C4 (229 x 324 mm, fits A4 flat). Square envelopes in 130 mm and 155 mm are also popular for cards.

How deep should the seal flap be?

A standard seal flap is 20-30 mm deep. Deeper flaps (30-40 mm) look more elegant and work better for self-seal and peel-and-seal closures. Shallow flaps (15-20 mm) save material but may not seal as securely.

CraftCalcs

Envelope Size Calculator \u2014 Dimensions for Cards & Documents

Calculate envelope dimensions needed for a given card or document size with clearance allowance.

Card/Document SizeSelect a preset or enter custom dimensions

Clearance

Gap on each side of the card

Card Width

Width of the card or document

Card Height

Height of the card or document

How We Calculate This

This calculator determines the minimum envelope dimensions for your card or document, adds clearance for easy insertion, and identifies the closest standard envelope size.

How it works

The envelope width and height are calculated by adding the clearance to each side of the card dimensions. The calculator then checks against standard UK envelope sizes to find the closest match that will fit your card.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always verify quantities before purchasing materials.