How to calculate area between graph line and average line?

Question

I have the following chart in Excel:

I want to calculate the area under the graph line.

Any idea?

Answer 1

For each adjacent pair of points, take average of y-coordinates, then multiply by difference of x-coordinates, and accumulate for all pairs.

Answer 2

For your related post (How to paint area under graph line with average line?) I suggested using a column chart. The area chart overemphasizes some points more than the values should allow. Since the points are discrete measurements, the sloping lines between measurements are meaningless, and calculating areas is going to be misleading.

So the "area" above the values is the sum of (value - average) for value > average, and the "area" below the values is the sum of (average - value) for value < average.

Very simple to calculate with two simple formulas.