How to Choose the Right Envelope Size for Your Greeting Cards

Quick answer

For a folded greeting card, choose an envelope about 3-5 mm wider and taller than the card. If you're posting within Australia, check the envelope fits Australia Post's standard letter size (up to 130 x 240 mm, 5 mm thick) or it may cost more to send. Buy envelopes and cards together when possible so the fit, colour, and finish already match.

A card that doesn't fit its envelope is a small problem with an outsized annoyance: you either fold it, force it, or make a second trip to the shops. Getting the envelope size right the first time is mostly about measuring the folded card, not the flat sheet, and knowing which sizes are practical to post.

This guide gives you a simple way to choose an envelope for cards, with the standard envelope sizes Australia buyers are most likely to encounter and the trade-offs between a snug fit, a roomy fit, and a postal-friendly fit.

Measure the folded card, not the flat sheet

Every envelope decision starts with one number: the folded size of your card. Take a card you've already folded and measure its width and height in millimetres. If you're making cards, fold first, then measure. A flat A4 sheet folded in half becomes roughly 148 x 210 mm, which is a very different envelope problem from the original sheet.

Once you have the folded dimensions, add a small allowance. An envelope should be about 3-5 mm larger than the card on both the width and the height. That gives the card room to slide in without bowing, but not so much room that it shifts around and creases in transit. If your card has a thick embellishment, wax seal, or ribbon, add extra depth rather than extra width.

• Measure the folded card in millimetres, then add 3-5 mm to width and height.
• For cards with wax seals or raised embellishments, check the envelope's depth or choose a slightly larger size.
• If you're unsure, cut a paper template to the folded card size and test it in the envelope before buying in bulk.

Common envelope sizes and what they suit

Most greeting cards sold in Australia fall into a few familiar folded sizes. A small card around 108 x 135 mm fits neatly in a C6 envelope (114 x 162 mm). A standard A6 card (105 x 148 mm) also fits a C6. A5 cards (148 x 210 mm) are usually paired with a C5 envelope (162 x 229 mm), and square cards need a square envelope because a rectangular one will either be too loose or too tight.

The C-series is useful because each size is designed to hold the next size down. That means if you standardise on C6 and C5 envelopes, you can cover most of your card-making or card-buying without guessing. For anything outside those sizes, measure and match rather than assuming a 'standard' envelope will work.

• C6 (114 x 162 mm) suits most small and A6 folded cards.
• C5 (162 x 229 mm) suits A5 folded cards and larger handmade cards.
• Square cards need square envelopes; don't force them into rectangular ones.

If you're posting, check the letter size first

The envelope that fits your card perfectly may not be the envelope that posts cheaply. Australia Post's standard letter rate applies to envelopes up to 130 x 240 mm and 5 mm thick, with a maximum weight of 250 g. A C6 envelope with a single card and a lightweight insert usually sits comfortably inside that. A C5 envelope with a thick card, ribbon, or wax seal can push past the thickness limit and move into a higher postage band.

Before you commit to a size for a mail-out, weigh and measure one filled envelope. If it's over the thickness limit, you have three choices: use a thinner card, use a smaller envelope, or accept the higher postage. Deciding this before you buy 100 envelopes is much cheaper than discovering it at the post office.

• Standard letter: up to 130 x 240 mm, 5 mm thick, 250 g.
• Thick cards, wax seals, and ribbons are the usual reasons a letter becomes a parcel.
• Test one filled envelope at the post office before a large mail-out.

Match the envelope to the card's finish and purpose

Size is the functional decision, but finish is the one people notice. A kraft envelope suits a letterpress card with a warm, handmade feel. A crisp white or coloured envelope suits a clean, modern card. If the card is a gift in itself, a slightly oversized envelope with tissue or a bellyband can make the unboxing feel more considered.

The practical trade-off is that decorative envelopes can be harder to write on, and dark envelopes may need a white gel pen or a printed label. If you're sending a batch, consider whether you want to hand-address them. A smooth, light-coloured envelope is easier to write on than a textured or very dark one.

• Kraft pairs well with letterpress and natural textures.
• Dark or heavily textured envelopes may need a label or white gel pen.
• If you're handwriting many cards, choose a smooth light-coloured envelope.

Buying cards and envelopes together

The simplest way to avoid sizing problems is to buy cards that already come with matching envelopes. Many greeting cards include a kraft envelope sized to the card, which removes the guesswork entirely. If you're buying a boxed set or a notecard set, check the product description for the included envelope size and count.

When you do need to buy envelopes separately, buy a small pack first and test it with your actual cards before committing to a larger quantity. Envelope sizing is one of those things that looks obvious on paper and becomes fiddly in practice, especially with handmade or unusually shaped cards.

• Check whether the card listing states the included envelope size.
• Buy a small pack to test before ordering in bulk.
• Keep a few spare envelopes in your two most-used sizes.

Decision rules for choosing an envelope size

• Rule 1: Match the folded card, not the flat sheet: Measure the card after folding and add 3-5 mm to both width and height. A card that is 108 x 135 mm folded needs an envelope at least 111 x 138 mm, which is why a C6 (114 x 162 mm) works well. If your envelope is less than 3 mm larger than the folded card, size up.
• Rule 2: Choose postal-friendly dimensions for mail-outs: Keep the filled envelope within 130 x 240 mm and 5 mm thick to stay at the standard letter rate. Thick card stock, wax seals, and ribbon are the usual culprits when a letter becomes a parcel. Test one filled envelope before buying in bulk.
• Rule 3: Prefer matched sets when the card design matters: Sets like the Spring Landscape 4pk Notecard Set include envelopes designed to match the cards. Substituting a different envelope can break the visual consistency, especially with scalloped or foiled edges. If the card has a distinctive finish, buy the matching envelope.
• Rule 4: Buy a small pack first when sourcing separately: Envelope sizing varies between suppliers and product lines. Order a small quantity, test it with your actual cards, then commit to a larger order once you know the fit. Never order 100 envelopes for a new card size without testing one.

Product facts that help with sizing decisions

• 3 Greeting Card: Hand lettered and hot gold foil printed card, 108 x 135 mm when folded, with a kraft envelope included. At 108 x 135 mm folded, this card fits a C6 envelope comfortably, and the included kraft envelope means you don't need to source one separately.
• Sixty (60) Greeting Card: Letterpress hot foil printed card, 108 x 135 mm when folded, with a kraft envelope included. Same folded size as the 3 Greeting Card, so if you're buying both, one envelope size covers them and they can be posted at the standard letter rate.
• Spring Landscape 4pk Notecard Set: Set includes 4 scalloped envelopes with 4 matching double-sided notecards, featuring a hot foiled gold print border and a gold-foiled address box on the envelopes. A matched set removes the sizing decision entirely, and the scalloped edge means you should not substitute a standard rectangular envelope if you want the set to look consistent.
• Mineral Green Luxury Satin Ribbon - 30 metres: 30 metres of soft double-faced silky satin ribbon in a self-dispensing gold foil printed FSC box. If you tie ribbon around a card or envelope, the added bulk can push a standard letter past the 5 mm thickness limit, so weigh and measure before a mail-out.

Who this guide is for

Best for

• People buying greeting cards who want to confirm the included envelope will suit their purpose
• Small business owners or makers sending cards by post within Australia
• Anyone matching envelopes to handmade or non-standard card sizes

Not for

• Buyers looking for international postage size rules outside Australia
• People seeking custom-printed envelope manufacturing advice
• Anyone wanting a full price comparison of every envelope brand

Choosing the right envelope comes down to one measurement and one postal check: the folded card size plus 3-5 mm, and whether the filled envelope stays within standard letter limits. When a card already includes a matching envelope, like the 3 Greeting Card or the Spring Landscape 4pk Notecard Set, that decision is made for you.