Right-Hand-Rule.
Point the thumb of the right hand in the direction of the current.
The tips of curled fingers will point in the direction of the magnetic field B.

B =( μo I)/ (2πr)
r perpendicular distance to the wire in m
Example
A long straight wire carries a current of 16 A.
The magnetic induction in a point is 4.0 x 10-5 T
Find the (perpendicular) distance to the wire
B =( μo I)/ (2πr)
4.0 x 10-5 = ((4π x 10-7 )( 16)) / (2πr)
(2πr)( 4.0 x 10-5) = 64π x 10-7
r = (64 x 10-7)/(8.0 x 10-5) = 0.08 m