Paddle Sizing and Fit
Greenland-paddle fit is usually determined by anthropometric (body) measurements. Please understand that these are "ball-park" measurements only. Experimentation and experience will help you to hone these measurements to find the perfect fit for you.
For a full-size paddle, a very common measurement is one-armspan plus a cubit (the distance from your elbow to your fingertips). Another common method is to ensure that you can just curl your fingers over the top of your paddle, with it standing vertically next to you. In windy areas, and for ease in maneuvering the paddle underwater, some people prefer a slightly shorter paddle of an armspan plus the distance from the wrist to the fingertips. "Storm" paddles (short paddles used with a full sliding stroke) are much shorter—being one armspan long and with the loom only one, two or three fists wide.
Blades can be as narrow as just over two inches to as wide as you can grip. For your first paddle, pick something between these two extremes and pick a width that is comfortable for you to grip.
The loom dimension must match your body and the kayak you are using. A method to find a good starting point is to stand, shake out your arms (relax), and allow your arms to hang at your sides. Lift your forearms so that they are parallel to each other and horizontal to the ground. Your arms should not be held against your sides—let them "float" (e.g., you should have enough room that a cloth rag stuffed under each armpit should fall to the ground rather than be held fast by arm pressure). Now make a "circle" with the thumb and forefinger of each hand. These circles indicate where the paddle-shoulders should be (where the roots of the blades begin).
Generally the loom must at least be as wide as your kayak—so if your kayak is much wider than a standard Greenland kayak you may have to improvise. Another method to determine loom length that involves your kayak is to sit in your kayak holding a broom-handle and discover where you hands naturally fall.
If you are uncertain about the loom size when making your first paddle, a conservative approach is to make the loom a little shorter than you think is right and the overall length of the paddle a little too long. You can then widen the loom (if necessary) and shorten the blades (if necessary) as you gain experience with the paddle. In this way you can slowly tweak it and discover a good fit. It's easy to take wood off, but not so easy to put it back on! Once you know your ideal paddle size you can skip this exercise.