There is a simple formula to calculate length contraction. It is somewhat like this:
L' = L/γ(v)
That is
L' = L√1-v²/c²
Where:
L is the actual length of the object.
L' is the length as observed by an observer who is in relative motion with respect to the object
v is the relative velocity between the observer and the moving object.
c is the speed of light.
Pretty simple.