Armpit to Armpit (A)

The most effective measurement is the pit to pit of a garment. This is taken by laying the garment flat, face up and measuring the cloth from
its widest point from under the armpit to the other armpit. The best way
to assess the measurement you require is to measure a garment of
similar description which fits you well (i.e. if you are buying a jumper
you should measure one you own and like the fit of to judge which
size you require when making your purchase). Never be misled
by your actual chest measurement, for example if your chest
measures 40 inches all around and you divide by two giving you
a pit to pit of 20 inches that would actually be too small
as you need at least one to two inches in a garment
to allow for movement.

Collar to Hem (B)

TThis is the measurement is taken from the bottom of the collar to the bottom of the hem on a garment. To obtain this the item must be laid flat but this time front down so you can measure the back. Again a good fitting equivalent item should be used to establish the measurements required.

Armpit to Cuff (C)

This measurement is taken from the inner arm, measuring from armpit to end of the cuff at the wrist on a long sleeved garment. Yet again it is recommended you take this measurement from a comparative item that fits you well.