When the dimensions of a painting or frame are written down or spoken, the long established and almost universally accepted rule is height x width. This is the method used by fine art retail galleries, art dealers, public museums, auction houses, picture framers, and restorers.
For example when you see a size as 16" x 20" (or 40 x 50cm) you know straight away that the painting is landscape orientation, and when the size is 20" x 16" (or 50 x 40cm) you know it is portrait format. This is even more important when a mount is used (on a watercolour or print for example), as mount borders are almost always slightly bigger at the bottom. Some antique frames (such as tabernacle of trophy frames) can only be used in one format.
For example when you see a size as 16" x 20" (or 40 x 50cm) you know straight away that the painting is landscape orientation, and when the size is 20" x 16" (or 50 x 40cm) you know it is portrait format. This is even more important when a mount is used (on a watercolour or print for example), as mount borders are almost always slightly bigger at the bottom. Some antique frames (such as tabernacle of trophy frames) can only be used in one format.
Many people think that it does not really matter which way round a size is, as long as you check every time someone gives you a size if the picture is landscape or portrait, or that every one who works with you knows which way round you record measurements. I think using the established format of HxW makes measuring paintings so simple and clear, and to me it makes sense that everyone in the art world uses this format to avoid embarrassing mistakes, and to not look slightly amateurish. For some reason many framing pricing programs, and computerised mount cutting software use width x height, which seems like very poor design indeed given that the art world standard is height x width.
Portrait Gallery by Richard Jolley Cartoonist.