When out shopping, sometimes you don't really want to try on a pair of pants to check if they fit. Whether there is a line at the dressing room or you're simply in a hurry, you need a method to determine size quickly. Because sizing seems increasingly arbitrary, having a rule of thumb is all the more useful. (Really Rag & Bone, your construction is superb, but your sizing is batty.)
Shopping with a friend Sunday, the topic arose at A.P.C. The salesperson, a very sweet cute woman, suggested that waist could be guessed by putting the waist of the jeans from the elbow to a fisted hand. While my friend was in the dressing room, we discussed it further. "How can that possibly work? If you gain weight the length from elbow to fist doesn't change?" Then I showed her my method, which has never failed me.
Facing the waist of the jeans toward you, place the jeans over your neck where a tee shirt collar falls. If the waistline of the pant will not meet on the back of the neck, the pant will not fit. Similarly, if there is overlap at the back of the neck, the pants will be baggy. This method takes into account that if your weight fluctuates (say from a 31 in summer to a 33 in winter), the fat of your neck increases in size proportionally to the rest of your body, including the waist.
After trying with a few pair, we found that the neck method seemed to work. It also makes far more sense than the elbow-to-fist. Any other methods out there?