To find the area under a curve using Excel, list the x-axis and y-axis values in columns A and B, respectively. Then, type the trapezoidal formula into the top row of column C, and copy the formula to all the rows in that column. Finally, determine the sum of the values in column C to find the area.
- List the x-axis values
In the A column, list the x-axis values of the graph using equal intervals, ensuring the use of the first and last data points. Increase the number of intervals listed to increase the accuracy of the final answer.
- List the y-axis values
In column B, list the y-axis values that correspond with the aligning x-axis value.
- Enter the trapezoidal formula
In column C, type in the following formula in the row corresponding with the first x-axis value: =(A2-A1)*(B1+B2)/2. The row numbers for both sets of values correspond with the starting row of the data points. Fill in all the rows in column C with this formula by clicking the box's fill handle and dragging down to the last row.
- Calculate the area
Delete the value in the last row of column C, then find the area by calculating the sum of column C. In an empty cell, type in =SUM(C1:C?), the question mark representing the number of the last row. The answer is the estimated area under the curve.