Concert (9" x 12") versus metric (229 x 305mm)

Apologies if this has already been addressed. I have searched the forum, but not seen anything about this specifically:

I exist in the metric world and regularly use the page size 229x305mm (as do all publishers I work with). I set my project up with said dimensions and it exports the PDF as 228.6 x 304.8mm (the mm equivalent to the 9x12 inch page size from which 229x305 is derived). I get that I’m splitting hairs over <0.5mm difference, but can I stop Dorico from overriding my project dimensions at print mode?


Since the “Arch” (Architect) paper sizes are actually a USA standard (9 x 12 is Arch A) I suspect the “true standard size” really is exactly 9 x 12in or 228.6 x 304.8mm, even if the metric world labels it as 229 x 305 for convenience.

Note - I can’t find the standards document where the Arch sizes are formally defined.

ISO 216 specifies a tolerance of plus of minus 2 mm for their “A” and “B” paper sizes. In real life “A4 paper” can be anything between 208 x 295 and 212 x 299mm. Since normal printing paper is not dimensionally stable anyway (the size changes depending on the humidity of the air) fractions of a mm are not significant.

Thanks Rob.

Yes, this is Arch A (or Arch 1). Everywhere I’ve seen it defined gives it in whole numbers, whether inches or mm (usually both, side by side). Fractions of a mm are not significant, fair, but my gripe is more that the print output doesn’t match the layout set up.

I will try another (random) dimension, that’s not so close to a preset, and see if it happens in other scenarios too. In reality, this all goes on a larger page and is cropped down anyways - but it’s good to establish what Dorico does and why, etc.

Looking inside an “A4” PDF produced by Dorico, the actual “page size” is specified in points, as required by the PDF standard, and is rounded to the nearest point, i.e. 595 x 842.

That actually corresponds to 297.04 x 209.90 mm (approximately).

There are 72 points per inch exactly, but since there are 2.834645669…etc points per mm, the “page size” in a PDF can’t be defined as an exact number of mm anyway.

Dorico also defines its page sizes in integral points, so Dorico’s idea of A4 is basically the same as PDF’s, i.e. it’s not precisely 210mm x 297mm, but it’s very, very close.

Thanks all!

Whilst humidity does affect size to some small degree, the reason for the ISO tolerance is likely to follow the constraints of trimming equipment in commercial printing. If you ask a printer to print to an A4 trim page size, you’ll get your pages +/- 2mm.