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.