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On the Wikipedia page https://en.wikipedia.org/wiki/Paper_size there are tables for standard paper sizes. The table "ANSI and CAN paper sizes" has paper size values expressed in inches and millimeters. For example, the ANSI D paper size is expressed as "22 × 34 inches" or "559 × 864 mm". But when you calculate the conversion by multiplying the inches values with 25.4 to get the millimeter values you get:

22 * 25.4 = 558.8

and:

34 * 25.4 = 863.6

So, is my calculation wrong or are the millimeter values on the Wikipedia page wrong? Because there is no mention about rounding on the Wikipedia page. (Assuming the ANSI paper sizes were originally defined as inches and then converted into millimeters).

user1580348
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    Given that there are no millimeter values with decimal parts on that page, I think it's safe to assume that all values are rounded to the nearest millimeter. –  May 31 '17 at 10:49

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Having written a good part of said article, I can confirm that we are trying to enforce a sensible number of significant digits. This usually results in rounding to the nearest millimeter.

From time to time, a random user believes that conversions should be more (i.e. overly) precise and hence changes one table or the other. Such edits may go by unnoticed for a while, so the article may not always be 100% consistent. The rounding policy isn't stated in the article explicitly, because it follows from Wikipedia's Manual of Style

I'm not sure whether ANSI or any other American standardization body specifies tolerances for paper sizes, but in ISO 216 and DIN 476 they are at least 1 mm and up to 3 mm for longer sides. That means, millimeter precision in conversions from inch values is arguably even too correct. Canadian standards rounded Letter etc. dimensions to the closest half-centimeter which might more accurately reflect actual American paper sizes.

The most common inch-based paper sizes are specified with a precision of half an inch. For other sizes, it rarely goes beyond a quarter inch, i.e. about 6 mm. Even if we assume a precision of half that for the definitions, we are still very well on the safe side in rounding converted metric values to the nearest millimeter.

Crissov
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