How to cut length pipe in 90 degree and 45 degree angle using formula and example calculation?

Based on the isometric drawing all pipe lgth will be deducted by the take off of the elbows.   

For degrees elbow and example" OD. Take off is =" x1.5 x.4 =mm

For degrees elbow and example  " OD. Take off is =" x . x.4 =. ormm