Calculate space with a progressive acceleration

How can I calculate the space my object will do in x seconds starting from velocity.y = 0 to -9.81?


EDIT:

Thank you for the answer but it doesn’t work, what about a not kinematic body? I’m using gravity.


EDIT2:

Probably I’m initializing the start velocity wrongly. I’ll try again later


EDIT3:

Yeah that’s working. I’ll try to be more explicit next time!

Distance travelled = (Initial velocity + Final velocity)/2 * Time

You might want to step through a basics physics course, such as http://www.physicsclassroom.com/class/1DKin/Lesson-6/Kinematic-Equations

try this one: Distance travelled = 0.5 * Acceleration * time^2

And in your case: Height = intitialHeight - 0.5 * 9.81 * time^2