I am putting together a fitted hauberk out of oversized panels of mail which require tailoring first, but I'm not sure if I should measure the mail at full expansion or not. For example, if I want a 46" chest on the hauberk, should I pull apart the rows or columns as far as they'll go before measuring 46" and cutting, or should there be a balance between horizontal and vertical expansion, or should there be as little expansion as possible (dense weave)? I want the finished hauberk to be tightly form-fitting if that makes a difference.

Thanks in advance

Somewhere in-between. ;) Presuming you're going to be slipping this on over your head, you may find that the largest measure you need isn't going to be your chest. If you can round up a friend with a measuring tape, have them measure around both biceps and your head while wearing any arming garment, aketon, etc., and holding both hands upright (touchdown!) over your head. Give that another 4 inches or so.

I should say relaxed.

Mail does not strech; It compresses when not used.
This means that if the mail is fitted when taut, it will not stretch to accomodate movement the way cloth will. So you need to make absolutely sure that the mail is either fully form fitted, (like a doublet, not merely removing the surplus rings) or leave enough space to move your arms freely.

If you have little previous experience with tailoring formfitting garment, I would recomend going for a simple solution rather than an ambitious one. Leave some extra slack across the chest and upper arms so that the mail does not snag when you are moving.

Thanks a lot for the replies. This has helped clarify my thought process and plan of work. It seems like the most important thing is to make sure mail will fit over the widest measurement of my torso (chest) while at full sideways extension.