Speed Formula
One way to calculate the average speed is to use math formula for speed. Speed formula is also known as average speed formula or speed distance formula or the formula for time distance and speed. Before we calculate the speed at which the lady below is running, let's define what speed is. Then we can calculate how fast the lady below is running or the average speed at which she is running at.
Definition of speed

Speed is an expression of the rate at which an object moves relative in a frame of reference. That means when you are calculating an average speed of something, you are assuming that the object is moving at a rate relative to a stationary place.
For example, the speed of a car is the rate at which the car is moving assuming that the road is stationary or non moving, even though technically the road is moving with the Earth. 
Physics formula for speed

The math formula for speed is distance divided by time. Or simply put, the average speed or how fast something is moving is the distance it has travelled divided by the time it takes to travel.
For example, the average speed at which the lady in the picture was running was given by the distance she has run divided by the time it took her to run that distance. 
Speed is scalar
When calculating average speed, note that speed is a scalar and not a vector. By scalar, we mean speed has no direction, unlike another physics term called the Velocity which has a direction. In another word, the speed at which a car is moving East at, say, 5 meters per second is the same as the speed at which the same car is moving West at 5 meters per second.

This makes calculating the average speed easy. The last thing we are going to mention about calculating speed is the unit of speed. 
What is the SI unit for speed?
The standard unit for speed is meter per second or m/s. That means when calculating average speed, measure the distance travelled in meters and measure the time taken to travel that distance in seconds then divide the distance travelled in meters by the time taken to travel that distance in seconds and there you have the average speed. If in doubt, refer back to the average speed formula; distance divided by time.
