Measuring a bit - from where?

[TiaPony]

I'm trying to buy myself a nice new replacement of my current bit - a loose ring 'lozenge' snaffle but I'm wondering how I measure the bit. Do I measure only the bit that is in her mouth (ie. up to the loose rings) or do I measure the whole mouthpeice including the bit attached to the rings?

Sorry if this makes no sense!
Thankyou

 

[Gentle_Warrior]

upto the loose rings

 

[TiaPony]

Thankyou