Frames sizes come in 3 prime units of measurement,
namely imperial (feet and inches) metric (centimetres) & the
International Standards Organisation (ISO) system . The ISO system
is sometimes mistaken as a metric system; in fact it is not, nor is
it Imperial, but is an established index of size
In the United Kingdom (UK) a commonly encountered
size is A3. This is double A4 and is easily printed with the ready
availability of larger printers
The dimensions of A3 are 16.5 inches x 11.7 inches
in imperial measurement, or 420mm by 297mm in metric. The key
characteristic of an ISO size is it retains its shape (aspect
ratio) when folded or doubled.
An A3 frame means that this size picture can be
framed by dropping the sheet into the insert area without cutting.
Frame sizes by convention refer to the area of picture to be
framed, which means (with the exception of borderless clip frames)
that the actual frame will be larger than the specified size. The
overall visible frame size can be estimated by adding the frame
moulding size less a 1/4" to the frame (insert) size.
Size A3 is a popular size for larger certificate
and image use, easily scaled, and gives a near 3 by 2 Aspect ratio
for photograph use. Due to its larger size, and hence
glass area, this is more prone to breakage than smaller frames, but
in transit this is minimised by well established packing solutions
utilised by Frames Online UK. The risk can be circumvented by
using styrene safety glass.