Superflat Letter Boxes

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Superflat mailing boxes, also called flat mailing boxes, large letter boxes or rigid mailers, are slim corrugated boxes with about 16mm of internal depth. They protect cards, prints, photos, CDs, cosmetics and flat apparel far better than an envelope, yet stay thin and light to keep postage low. Choose from 14 sizes from 140 x 80mm to A3 440 x 320mm, in white, brown kraft, black, rose pink and mint blue, plus white tuck front versions.

16mminternal depth (most sizes)

14sizes

5colours

25 – 500boxes per pack

Find your size

Eight superflat boxes drawn to the same scale, seen from above. Tap a box to shop it.

B161140 x 80 x 16 B8180 x 100 x 16 B22220 x 160 x 16 B109280 x 192 x 16 B21310 x 220 x 16 B412335 x 335 x 16 B102360 x 250 x 20 B198440 x 320 x 20

Superflat mailing box sizes and colours

Inside (mm)	Colours & codes	Good for
140 x 80 x 16	B161	Gift cards, jewellery, keyrings
152 x 132 x 16	B1 B280 B351	CDs, cards, patches, stickers
180 x 100 x 16	B8 B295 B276 B348 B27 tuck	DL cards, phone cases, cosmetics
192 x 125 x 16	B10	Cards, photos, small prints
198 x 146 x 16	B213	A5 cards and booklets
220 x 160 x 16	B22 B296 B278 B447 B349 B36 tuck	A5 prints, notebooks, flat apparel
270 x 220 x 16	B63	Calendars, art prints
280 x 192 x 16	B109	Books, planners, documents
310 x 220 x 16	B21 B297 B279 B448 B350	A4 prints, certificates, flat clothing
310 x 230 x 16	B37 tuck	A4 items, premium tuck finish
335 x 335 x 16	B412	12-inch vinyl records
350 x 250 x 15	B9	Large prints, documents
360 x 250 x 20	B102	B4 documents and prints
440 x 320 x 20	B198	A3 prints, posters flat, artwork

Sizes are internal, length x width x depth. Tap a colour to shop that box. Going by post as a large letter? Check Australia Post’s current letter size and weight limits against the outside of the packed box.

Why choose a superflat box?✓ Rigid board stops bending, creasing and crushed corners✓ Thin profile for large-letter style items✓ Lighter and cheaper to post than a full-height box✓ Folds together with no tape needed to assemble✓ Recyclable cardboard, no plastic bubble needed

Packing flat items

1Measure Check the length, width and thickness of the item. Most of our superflats take up to 16mm.

2Protect the surface Slip prints and photos into a zip lock bag or tissue first.

3Close & label Fold the lid in, seal with tape or a sticker, and add a label.

Compare box styles: Diecut mailers Tuck front Self-seal Full colour Book wraps Shipping cartons Medium & large Heavy duty Long boxesNot sure which size? Try the Box Finder or see the box & carton guide. For books that need more depth, try book wrap mailers.

✎ Custom printed boxes✉ Free samples on request⚑ Pick up Minto NSW / Braeside VIC✈ Free Sydney / Melbourne metro delivery over $500↻ 90-day hassle-free returns

Superflat mailing box FAQs ▾

Superflat mailing box FAQs

What is a superflat mailing box?

It is a slim diecut cardboard box with about 16mm of internal depth (15 to 20mm on a few sizes). It works like a rigid envelope that protects flat items from bending and crushing.

Can I post a superflat box as a large letter?

Often, yes. Australia Post sets size and weight limits for large letters, so measure the outside of your packed box and weigh it, then check the current limits with Australia Post before you post.

What fits in a 16mm superflat box?

Greeting and gift cards, art prints, photos, CDs, patches, stickers, phone cases, slim cosmetics, socks and flat-folded t-shirts.

What size superflat do I need for A4 or A3?

For A4 use 310 x 220 x 16mm (B21 and colours) or the 310 x 230 x 16mm tuck (B37). For A3 use 440 x 320 x 20mm (B198). B4 documents (250 x 353mm) fit the 360 x 250 x 20mm (B102).