How do you find the B field between finite wires?

[Frostfire]

I know the results for infinite, but how about finite? And where is the cutoff with the aproximation of infinite? I've heard the value 10% tossed around is that right?

 

[graphene]

if u have used bio savart law to find the field of an infinite wire, u wud have integrated along the comple length (infinite) of the wire.
now just integrate along the finite ength of the wire