Elbows are fittings that attach to the downspout.
One end of the gutter elbow is crimped so that it can fit inside another elbow or downspout.
Two elbows are required per downspout assembly and a third may be used at the bottom; Two elbows coming from the gutter are used to span the length of the eave so the downspout can be directly mounted to the wall of the structure and one is used at the bottom of the downspout at ground level to direct drainage in a particular direction.
So calculate three elbow per outlet for a house with no cantilever (however additional two elbows in cases where you have cantilever)
An “A” style elbow refers to an elbow that, when attached to a downspout, angles the downspout frontwards and backwards.