To calculate the square meters of a duct you must add the total length of the straight duct work plus the loss of length from the elbows. A standard elbows measurement is 15 feet for each elbow with a 4 inch diameter or 20 feet for an elbow with a 6 inch diameter.
A= 2*(w+h)*(l1+l2) W=width H=Height L1, L2 Length of Elbow
The length of your forearm from inner elbow to wrist.
stays the same length
The formula used to calculate the surface of a 90 degree elbow is pi^2 *. This formula is taught in geometry class.
The length from your wrist to your inside elbow