Gigapixel AI setting width and height for A3

I can’t seem to find a way to convert Width and Height to give A3. Any hints, please.

Most paper suppliers give the metric size of an A3 sheet as 42.0cm x 29.7cm in landscape orientation.
This converts to 16.53" x 11.69", however the paper suppliers generally quote it as 16.5" x 11 3/4".

Without cropping, Gigapixel maintains the aspect ratio of the source image, so for example, using the metric values, you can either set the Width to 42.0 and the units to cm, or set the Height to 29.7cm and the units to cm. In either case you also need to specify the Pixels per Unit. For example a setting of 118.11 px/cm is the same as 300px/inch. If you use that setting, it would translate to an image that was 4961px wide (or if you used the height, 3508px high).

The aspect ratio of an A3 sheet (using the metric values) is 42.0/29.7 = 1.414 : 1
If your source image has a different aspect ratio then it will have to be cropped. Gigapixels custom crop only allows the entry of a two digit integers for the aspect ratio, and for that reason I would opt to either crop the source image, or the resized image in other software that has better cropping functionality.