What Envelope Size Do I Need? Envelope Sizes Explained

Envelopes are one of those things you don’t really think about… until you need one that actually fits.

That’s usually when it turns into a bit of a guessing game… folding documents, trying different sizes, or ending up with something that doesn’t quite sit right.

Once you understand how envelope sizes work, it’s actually very straightforward to get right first time.

This guide breaks down the most common envelope sizes in the UK so you can quickly choose the right one for what you’re sending. We print and dispatch thousands of items every week, so getting sizing right is something we deal with day in, day out.

Why Envelope Sizes Can Feel Confusing

Envelope sizes aren’t always obvious at first. You’ve got C4, C5, DL… and unless you deal with print regularly, it’s not always clear what each one is actually for.

That’s usually where a bit of guesswork creeps in… folding documents more than needed or picking a size that doesn’t quite feel right when it arrives.

It’s not a major issue… but getting it right makes everything look cleaner, neater and more professional.

How to Get It Right First Time

The easiest way to look at envelope sizes is to work backwards from what you’re sending.

Instead of trying to remember what C4 or DL means, just think about your document… does it need to stay flat, or can it be folded?

Once you’ve got that clear, choosing the right envelope becomes straightforward. You’re simply matching the size to how the document needs to arrive.

Here’s how the most common envelope sizes break down…

Envelope Sizes Explained

C4

Designed to fit A4 without folding. If you want documents to arrive flat and looking clean, this is the one to use.

If you’re sending things like contracts, presentation packs or printed brochures, C4 keeps everything flat and looking exactly as intended.

C5

A solid all-rounder. Slightly bigger than A5, or a good fit for A4 folded in half. You’ll see these used for letters, invitations and anything that needs a bit more space without going oversized.

In business, they’re a go-to for longer letters or documents where folding once keeps things looking tidy.

DL

You’ll recognise these straight away… they’re used for most standard business post.

You’ll see these used all the time for invoices, statements and direct mail campaigns… especially when paired with window envelopes.

C6

One of the smaller sizes. Not as common day to day, but useful for postcards, invites or smaller inserts.

Handy to have if you’re sending compact items and don’t want excess space in the envelope.

Square

Used for square formats like greeting cards and invitations. Less common in everyday post, but useful when your print doesn’t follow standard sizing.

Worth noting… these can sometimes cost more to post due to their shape.

Envelope Size Guide

If you prefer a quick reference, here’s how the main envelope sizes compare:

If you’re unsure, focus on what your document needs… keeping it flat or folding it neatly will usually point you to the right size.

Need Printed Envelopes?

If you want envelopes that actually match your print, we can help. From everyday business use to full direct mail campaigns, we’ll make sure everything lines up and looks spot on.

Need something more specific? We can sort that too… custom sizes, finishes, whatever works for your job.

Get your custom quote… no fuss, no faff.