A line's slope, or gradient, describes the extent of its slant. If its slope is 0, the line is completely horizontal and is parallel to the xaxis. If the line if vertical and parallel to the yaxis, its slope is infinite or undefined. The slope on the graph is a visual representation of the variable y's rate of change with respect to x. You can therefore calculate the slope by determining this rate of change from any two points on the line.

Identify the points' coordinates. For this example, imagine that the points have coordinates of (2, 8) and (4, 3).

Subtract the second point's ycoordinate from the first's: 8  3 = 5.

Subtract the second point's xcoordinate from the first's: 2  4 = 2.

Divide the difference between the ycoordinates by the difference between the xcoordinates: 2 ÷ 5 = 0.4. This is the line's slope.