Select two points on a graphed line between which you wish to determine the slope. Record the coordinates for each point in the (x, y) format on a slip of scratch paper. Write the position of each point along the horizontal axis first, followed by the position of each point along the vertical axis.
Calculate the change in y. Subtract the second y coordinate from the first y coordinate. Record the result in the numerator section of the slope formula (the part above the line).
Calculate the change in x. Subtract the second x coordinate from the first x coordinate. Record the result in the denominator section of the slope formula (the part below the line). The resulting fraction is one way of representing the slope (rise over run). To represent the slope as a decimal instead, divide the denominator (the run, or change in x) into the numerator (the rise, or change in y).