Which Envelope Do You Choose? C5, C6, A4, and Bubble Lined Envelopes Compared
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by Verpakkingdeals.nl
6 min reading time
C6, C5/C6, C5, or A4: which envelope size is right for which mail item? And when is it better to choose a padded envelope or a letterbox box? Including maximum letterbox dimensions for PostNL and DHL.
Choosing an envelope seems simple until you receive a package back for the third time because it just didn't fit through the letterbox. Or until you put a piece of jewelry in a paper envelope and the customer receives a dented product. In this article, we list the standard sizes, explain when it's better to choose a padded envelope or a box, and what exactly does and does not fit through a letterbox.
Standard paper sizes at a glance
Paper envelopes follow the C series, which aligns with the well-known A series of paper. The logic is simple: each C-size is slightly larger than the A-size with the same number, so the paper fits in without creasing.
Envelope
Dimensions
What fits inside
C6
114 x 162 mm
An A6 card, or an A4 folded twice
C5/C6
114 x 229 mm
An A4 folded into three
C5
162 x 229 mm
An A4 folded once in half
A4 envelope
229 x 324 mm
An A4 unfolded
C6: cards and short letters
The C6 is the classic card size. A birthday card, thank you card, or A6 flyer fits perfectly. If you want to include a letter, you fold the A4 twice. For webshops, this is the format for a handwritten thank you note with an order. The C6 White Envelope 114x162mm in a pack of 50 costs € 4.00.
C5/C6: the letter you fold into three
The elongated format you know from bank statements and invoices. You fold an A4 into three, and it fits. This is the most commonly used format for business mail, precisely because the fold aligns neatly with a windowless or windowed envelope. You can find it here as C5/C6 White Envelope 114x229mm, 25 pieces for € 4.00.
C5: one fold and done
Do you have multiple sheets, or do you not want an offer or certificate to have three fold lines? Then the C5 is more logical. An A4 fits with a single fold, and there is room for a stack of paper. The C5 White Envelope 162x229mm, 25 pieces is priced at € 4.95.
A4 envelope: no fold at all
Contracts, diplomas, posters, calendars: anything you don't want to fold goes into an A4 envelope of 229 x 324 mm. See the A4 Envelopes 229 x 324mm, 10 pieces for € 4.00. If you want something sturdier and with a self-adhesive sealing strip, the Envelope With Adhesive Strip A4 262x371mm, 5 pieces in beige (€ 2.00) is an option: larger than a standard A4 envelope, so also suitable if an insert card or multiple documents need to be included.
As soon as you send something thicker than paper, or something that can break, scuff, or dent, paper stops being suitable. A padded envelope (also called a bubble envelope) has a layer of bubble wrap on the inside and absorbs shocks. Think of jewelry, phone cases, cosmetics, USB sticks, small electronics, books, and CDs.
Practical rule of thumb:
Flat and unbreakable (paper, cards, stickers, textiles): paper envelope is fine.
Small but fragile (glass, electronics, jewelry): padded envelope.
Scratch-sensitive (books with dust jackets, trading cards): padded envelope, because paper can scuff.
Do you send more often and want the package to stand out? The metallic bubble envelopes are available individually in several sizes: 21x14 cm (€ 0.80), 22x17 cm (€ 0.90), 20x26 cm in green (€ 0.90), 33x23 cm (€ 0.80) and 44x32 cm in purple (€ 0.90). Handy if you buy small quantities or want to vary per order.
When is a box better than an envelope?
An envelope is flexible, and that's precisely the problem when the contents are not. Choose a box if:
the contents are hard and fragile and should not bend (glassware, frames, ceramics);
you send multiple loose items that would otherwise shift against each other;
the contents are thicker than approximately 2.5 cm and you still want it to fit through the letterbox: an envelope bulges, a letterbox box maintains its size;
you want a neat unboxing experience, for example with gift items.
This is where things often go wrong in practice. For PostNL and DHL, letterbox mail has a maximum of 38 x 26.5 x 3.2 cm and 2 kg. All three measurements count: if your shipment is 2 mm too thick, it becomes a parcel, with the corresponding rate and delivery method.
What to pay attention to:
Measure the thickness with contents inside. An empty padded envelope is thin, a filled one bulges. Place a ruler along the thickest point.
Account for the bubble layer. A padded envelope itself quickly adds several millimeters to the thickness, on both sides.
Fill without bulging. Filling space is good, overfilling pushes the envelope past 3.2 cm.
In doubt? Choose a custom letterbox box. It is designed to stay within the limit and remains flat.
To protect the contents within that 3.2 cm, you can fill it yourself with bubble wrap. The Bubble Wrap Roll 500 mm x 500 m costs € 12.95. If you want to make it visible whether a shipment has been opened during transit, the Security Seal Stickers "VOID", 60-pack (€ 9.95) are a cheap addition.
Briefly summarized
Card or A6: C6.
A4 folded into three: C5/C6.
A4 with a single fold or multiple sheets: C5.
A4 unfolded: A4 envelope.
Fragile or thicker than paper: padded envelope.
Hard, fragile, or just too thick: letterbox box.
Still unsure which size suits your products? View the full range in the collections Envelopes, Padded Envelopes and Letterbox Packaging. If you can't figure it out, or want to know what makes sense for larger quantities? Email your question with the dimensions and weight of your product to info@verpakkingdeals.nl, and we'll help you determine the right size.
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