The international sizes can be expressed in inches in dozenal quite accurately as:
Of course, one needs a ruler with twelfths of inches! The sizes given are in ratio 2 : 1 with an error of only 0·015 per gross (0·007%).
These proportions are of at least equal accuracy with millimetric sizes, but do not depend on such tiny units. If we use lines, which are twelfths of inches (more than twice as large as millimetres), the sizes are:
Using the reflected 3 (rather than E) for eleven the rotational symmetry of the typewritten numbers for A4 is remarkable and makes it easy to remember! It is very satisfying to find these sizes coming out more simply in dozenal inches than in decimal metric ...