I am creating svg documents in Inkscape to print on an Epson color printer, and using layers in the same svg with Lightburn to cut in cardstock on a laser cutter. I am using US Letter size paper but use mm for measurements.

I can use the Inkscape measure tool and check the outside dimensions of the set of tiled cards. I get a width of 186.04mm and height of 260.67.

The cutting part works just fine. My cuts measure exactly the same as in Inkscape.

However, when I print (whether from Inkscape directly or first saving as pdf then printing from Windows 10 to the Epson 2800 series printer) my measured outside dimensions are slightly less, about 180.5mm wide and 253.5mm high. This obviously doesn't match  up (I'm trying to register the printed material precisely with the cuts). What's truly odd is that this imposed scaling is not even the same for width and height. I do have scaling turned off in the print options.

My workaround is to scale the cut document to the measured size of the print in my cutting software (Lightburn). It looks odd  that the document properties show the mm per user unit as 101.5999 but that's just 4 inches in mm (rounding up a wee bit).

I'm just wondering if there's a better way to do this? Perhaps it's just an issue with this particular printer.

I'd ensure that printing to the Epson, the pdf print dialog has "Actual size" or "100%" selected.

A typical mm document in Inkscape has a uu scale of 0.264583. I'd set up a new document with that scale (easy with any A4 template, changing only the page size for your stock), then paste/resize your artwork in the new document. 

Yes, I did ensure that the Epson print dialog (whether printing from Inkscape or after saving to pdf and printing from Acrobat reader) was set to actual size.

Interesting idea with the A4 template setup - I'll give that a try. Thank you for the suggestion!