Once the workshop and model of armor are chosen, measures are needed. In order to get fitting and convenient armor, one point should be taken into account, namely that all measurements have to be taken while the client is wearing quilted jacket and pants (underarmor clothes). In this case the armor will fit perfectly.
The second point is that professional blacksmiths have a special form for measurements. It describes, in a very detailed way, how to take measurements (there’s a picture of a man with arrows indicating where and how to measure). For example, armor workshop «Age of Craft» provides this form via their website http://ageofcraft.com/. Practice shows that this method of taking measures can be used even by a novice. If you have questions, contact the workshop and they can even make a video explaining how to take measures. The quality and convenience of armor will not be affected by the fact the whole procedure takes place elsewhere. The only thing that may cause problems is a sloppy approach to measurements by the client. However, for professional gunsmiths, it is not a problem and size discrepancies (within 2-3 centimeters) are eliminated on the spot, in the field.