how to find the area under a graph

[chogga]

i need help in finding the area under the graph in excel as it is a
complicated curve for the pressure vs volume of a combustion chamber

 

[PY & Associates]

How does your curve look like please?

 

[Jerry W. Lewis]

See
http://www.stfx.ca/people/bliengme/ExcelTips/AreaUnderCurve.htm
for a couple of simple approaches to numerical integration.

If you know the formula for the curve, you might try integrating it
analytically. Similarly, you could integrate a polynomial (or other)
approximation to the curve.

Jerry