Look at the size of the column or beam from the drawings.
Adopt Dia of the bar (generally 8mm Dia is used for stirrups).
Deduct the concrete cover or clear cover.
Find the total outer length of the stirrup after deducting the concrete cover.
Add the length of the hook to the length of the stirrup.
Deduct the length of bends.
Use the below formula to find the total cutting length of stirrups.
Cutting Length of Stirrups = Perimeter of Shape + Total hook length – Total Bend Length.