Mailer boxes have become the default packaging for e-commerce. They ship flat, fold up without tape, survive the courier network and give you a full printable surface for branding. But choosing the wrong size, flute or print method can quietly add 20–30% to your packaging bill.

This guide covers the three decisions that matter most: sizing, materials and printing.

1. Getting the Size Right

Mailer box dimensions are always written as length × width × height, measured on the inside of the box. Using outside measurements is the most common and most expensive mistake — your product arrives and simply does not fit.

How to measure correctly

  • Length — the longest side of the opening
  • Width — the shorter side of the opening
  • Height — the depth from the base to the top edge

Add roughly 5–10 mm of clearance on each dimension for the product itself, plus extra space if you are using tissue paper, void fill or an insert. Then check the final size against your courier's dimensional weight rules — a box that is one centimetre too tall can push you into the next shipping band on every single order.

2. Choosing the Material

Almost all mailer boxes use corrugated board. The flute grade determines both strength and thickness:

  • E-flute (about 1.5 mm) — thin, smooth and the best surface for high-quality printing. Ideal for apparel, cosmetics, accessories and most subscription boxes.
  • B-flute (about 3 mm) — noticeably stronger with better cushioning. The right choice for heavier goods, glassware or anything fragile.
  • EB double wall — maximum protection for heavy or high-value shipments, at a higher cost and volume.

For the outer surface you can choose white coated board for vivid full-colour printing, or natural kraft for a warmer, more sustainable look that also hides scuffs from transit better.

3. Choosing the Print Method

Method Best for Notes
Digital Small runs, frequent design changes No plate cost, full colour, higher unit price
Flexo Large runs, 1–3 spot colours Very low unit cost at volume, simpler artwork
Offset (litho-lam) Photographic artwork, premium retail Best image quality, highest setup cost

A practical rule: below roughly 500 boxes, digital almost always wins. Above a few thousand with a simple design, flexo becomes dramatically cheaper per unit.

What Actually Drives the Cost

  • Box size — you pay for board area, so oversized boxes waste money twice (material and shipping)
  • Order quantity — setup costs spread across the run, so unit price drops sharply with volume
  • Number of print colours — each additional spot colour adds a plate and a pass
  • Finishes — matte lamination, spot UV, foil and embossing all add cost but lift perceived value

Before You Place the Order

Request a physical sample and pack your real product into it. Check that the lid closes cleanly under load, that the print colour matches your brand and that the box survives a realistic drop test. Fixing a sizing error at sample stage costs nothing; fixing it after 5,000 boxes are printed costs a lot.

Send us your product dimensions and target quantity and we will recommend a suitable size, flute and print method — along with a free design proof.