Our default option, when scaling images supplied to us for printing is to resize your image to fit within the dimensions of the size you’ve given us, this will give you the closest size possible without artworking or cropping your image.
Here are some examples for different proportioned images if you ordered an A3 (420 x 297mm) print and asked us to resize the image for you.
A square image would fit in to an A3 sheet in either landscape or portrait, the width and height would be defined by the shortest dimension of A3 (297mm) and produce a 297 x 297mm image.
This thin rectangle image does not proportionally scale to A3, therefore the width is defined by the longest side of A3 (420mm), the height will then be scaled proportionally and be shorter than A3. The print size of this particular image is 420 x 168mm.