Instantaneous velocity is obtained from average velocity by shrinking the difference in times (delta t) closer and closer to zero. We eventually reach a limiting value which is known as instantaneous velocity. If we would create a graph of velocity vs. time for an object, we could derive the instantaneous velocity by taking the slope of a line tangent to any point on the curve (of that velocity). However, we won’t be calculating Instantaneous Velocity through a graph if we want to use it inside our programs. So, we will need some basic Calculus to find this velocity. Here is the formula for Instantaneous Velocity:

see http://www.gamedev.net/reference/articles/article434.asp

for the actual formula

v = d/t

velocity (m/s) = distance(m)/ time(s)

unless you are given with different units