B4 paper size and dimensions

B4 sits between A4 and A3. That makes it just big enough for a stack of A4 with a little room to spare, without the item becoming unwieldy. For post it has another role: it marks the largest size that still counts as a letter.

B4 in every unit

B4 in pixels

At 300 dpi, a B4 area needs 2953 × 4169 pixels. With 3 mm of bleed, the document size is 256 × 359 mm, which is 3024 × 4240 pixels.

B4 as an envelope

A B4 envelope is the classic choice for anything too thick for C4: application folders, catalogues, documents in a clip file or a C4 envelope with a reply envelope inside. For several centimetres of content, there are gusset envelopes with a base that open out like a small box.

B4 is the limit for letters

With Royal Mail, a Large Letter may be at most 353 × 250 mm. That is exactly B4. Deutsche Post applies the same maximum to its Großbrief and Maxibrief. Anything bigger goes as a parcel.

After that, weight and thickness decide the postage. A well-filled B4 gusset envelope soon exceeds the 25 mm of a Royal Mail Large Letter or the 20 mm of a German Großbrief. Details for Germany are on German letter sizes.

B4 on the copier

To enlarge A4 to B4, use 119 %. To reduce A3 to B4, use 84 %. Copiers often show 122 % and 86 % instead. Those values are for Japanese JIS B4 at 257 × 364 mm, a common copy size in Japan.

Frequently asked questions