Horizontal Range 

It is defined as the horizontal distance covered to the maximum distance possible.

The horizontal range is a distance (OB) is:

OB = Horizontal component of velocity(u_x) * Total time(t)   

(u_x = u cosθ and t = 2usinθ/g)

That is, Range(R) = ucosθ * 2usinθ/g     

Horizontal Range of the projectile is:

Horizontal Range(R) = u2sin2θ/g  

( sin2θ = 2cosθsinθ )