Rather than trying to use a tape to measure, I use my hand and that allows me to feel how straight and how long the keel is at once. I call a keel that is from the heel of my palm to the tips of my fingers good length. It isn't so much a defined length but more comparative that I go by. In fact, when you look at traits like length of keel, length of back, width of breast and so forth, those are all comparative terms. The only thing I weigh or measure is weight of birds.