Which "rule of thumb" do you use for prey size?

[Vypyrz]

I voted for girth however I do weigh every item and try to keep them about 10% often they are close to the same anyway.

I do 10-15% of the snakes body weight until 1000g then I just feed a small rat once weekly.

I use a combination of these two depending on which snake it is and all of mine get fed every 10 days...