To find the time of flight, determine the time the projectile takes to reach maximum height. The time of flight is just double the maximum-height time.

Start with the equation:

v_{y} = v_{oy} + a_{y} t

At maximum height, v_{y} = 0.

The time to reach maximum height is t_{1/2} = - v_{oy} / a_{y}

Time of flight is t = 2t_{1/2} = - 2v_{oy} / a_{y}

Plugging in v_{oy} = v_{o} sin(q) and a_{y} = -g, gives:

Time of flight is t = 2 v_{o} sin(q) / g

where g = 9.8 m/s^{2}

The time of flight is also determined solely by the initial velocity in the y direction and the acceleration due to gravity.