Montage Dimensions

[anthony]

It is not directly posible to specify the final size of a montage.
Also to specify a size in real world units you will need to set a final density to the output image.

The best solution is to play with the -geometry setting and -tile so as to
generate an image as close to the size desired as you can.

If that image is a little smaller you can filter the result thorugh a second convert command to add a border or fill to a specific size and as a bonus set the resolution density correctly for the right real world units you are using.

More deatils of montage options are availabel in IM Examples (see signature).