What is a standard mailer box size?

There is no industry standard size. A mailer is specified from three numbers — internal length, width and depth — plus a clearance per side. Most projects use 3 to 5 mm of clearance on each side and 2 to 3 mm on the depth, then round to the nearest sensible millimetre.

Should I choose E-flute or B-flute for a mailer box?

E-flute is about 1.5 to 1.8 mm thick, gives the flattest print surface and folds to a tighter edge, so it suits retail-style mailers and lighter products. B-flute is about 3.0 to 3.2 mm and absorbs more handling, which suits heavier products or longer parcel routes. Both are available on every mailer design in this catalogue.

How many mailer boxes fit in a 40HQ container?

It depends on the carton, not the box. Divide the container's usable volume — about 68 m3 for a 40HQ at 85% loading efficiency — by the carton volume, then multiply by the flat-packed mailers per carton. A 60 x 40 x 40 cm carton is 0.096 m3, so a 40HQ holds roughly 708 of those cartons.

Does board thickness change my shipping volume?

Yes, but only on the outside. If your 30 x 20 x 8 cm dimensions are internal, E-flute at 1.5 mm adds about 3 mm to each axis and B-flute at 3 mm adds about 6 mm. On a 30 cm length that is the difference between 30.3 cm and 30.6 cm external — small per box, but it compounds across a full container.

Mailer Box Sizes, Board Grades and Container Loading

A reference for procurement: how to specify a mailer's dimensions, what E-flute and B-flute actually measure, and how box size turns into cartons, cubic metres and container loads.

1. There is no standard mailer box size

Mailer boxes are made to your dimensions, not picked from a stock list. Every quote starts from three numbers — internal length, width and depth — plus the clearance you need around the product.

Dimension	How to set it	Common practice
Internal length	Product length + clearance on both ends	3–5 mm per side
Internal width	Product width + clearance on both sides	3–5 mm per side
Internal depth	Product depth + insert thickness + clearance	2–3 mm extra
Board thickness	Adds to the outside only, not the inside	E-flute +3 mm per axis, B-flute +6 mm

State the dimensions you send as internal. That is the convention in packaging quotations, and it is the number your product has to fit into. If you measure a sample you already have, measure the inside face to face.

2. Board grades: what the flute actually measures

Three flute profiles cover almost every printed mailer. The figures below are industry-standard ranges, not a single supplier's specification — thickness varies by liner weight and by mill.

Flute	Board thickness	Common strength grade	Print surface	Best for
E-flute	1.5–1.8 mm	32 ECT single wall	Smoothest — sharpest detail and small type	Retail mailers, cosmetics, light products
B-flute	3.0–3.2 mm	32–44 ECT single wall	Good — slightly softer edge	Heavier products, longer parcel routes
C-flute	3.2–3.9 mm	32–44 ECT single wall	Coarser — larger areas only	Shipping cartons, not retail mailers

Two consequences that show up on every quote:

Thicker board folds to a larger outside. A 30 × 20 × 8 cm internal mailer becomes roughly 30.3 × 20.3 × 8.3 cm outside in E-flute, and 30.6 × 20.6 × 8.6 cm in B-flute.
Thicker board costs print fidelity. E-flute holds fine type and hairlines; B-flute tends to fill in below about 6 pt on reversed-out artwork.

3. From carton to container

Freight is charged on the carton, so the number you actually need is carton volume, not box size. The chain is four steps:

Carton CBM = length × width × height in cm ÷ 1,000,000
Cartons per container = usable container volume ÷ carton CBM
Mailers per container = cartons per container × flat-packed mailers per carton
Chargeable weight = the greater of actual gross weight and volume ÷ 6,000 (air) or ÷ 5,000 (express)

Container	Typical usable volume	At 85% loading	Worked example: 60 × 40 × 40 cm carton (0.096 m³)
20GP	28 m³	23.8 m³	≈ 248 cartons
40GP	58 m³	49.3 m³	≈ 513 cartons
40HQ	68 m³	57.8 m³	≈ 602 cartons

Read those three figures as an illustration, not a promise: cartons rarely stack to the roof, pallets take space, and a mixed order never fills a container cleanly. At 50 flat-packed mailers per carton the same example works out to about 12,400 mailers in a 20GP and 30,100 in a 40HQ.

Run your own numbers instead of trusting a rule of thumb — the carton, CBM and container calculator takes carton size, units per carton and order quantity and returns cartons, total CBM, volumetric weight and container fill.

4. What this catalogue actually quotes

Mailer designs listed	22 corrugated and kraft designs, printed inside and out
Minimum order	18 of the 22 designs start at 300 pcs; some designs start at 100 pcs
Board options	E-flute or B-flute, kraft or white top liner
Closure	Tuck flap as standard
Sample lead time	3–7 days
Bulk lead time	12–15 days
Print	Full colour outside and inside; hot foil, spot UV, embossing, matte or gloss lamination available

5. What we need to quote a size

Internal length × width × depth, in mm or cm
Product weight, and whether it ships by air or sea
Quantity — and whether you want flat-packed or assembled
Artwork, or a reference photo if you do not have artwork yet

Send those four things and you get a dieline, a 3D mockup and a quotation. If you are still choosing a structure, the rigid vs folding carton comparison covers where a mailer sits against the alternatives, and the MOQ and lead-time guide explains how quantity changes the unit price.

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Quote a mailer box size →Calculate cartons and CBM →

Board thickness ranges follow FEFCO-style flute profiles and are given as industry ranges, not as one mill's specification. Container capacities are nominal figures; usable volume assumes 85% loading. Facts reviewed 30 October 2026.