I heard this tip from a baker friend of mine who said this was an activity she was made to do in culinary school. I think especially for bakers and pastry cooks, measurements are particularly important. You need to know how thick to roll your cookies or how long to roll your dough. The problem is you might not always have a ruler handy or some pastry chefs actually prefer that their cooks not use rulers as that can waste time.
So that’s when knowing the measurements of particular body parts ie. fingers, handspan, and even ears come in handy. I just did this the other day, but I took a tape measure and found particular parts of my hands that matched necessary measurements the best. For example, the last notch of my middle finger to the tip is exactly 1 inch. My full handspan is about 7 3/4 inches, which is not exactly useful, but then I realized my ears (going up and down) were exactly 3 inches, so that maybe useful when I need something a half a foot. Right, so you definitely have to do some exploring, but you’ll be surprised at how closely you can get some of the measurements.