A spreadsheet model of a fuel cell was developed for use during the early stages of stack design and development. The model uses a plot of cell potential versus current, referred to as a polarity plot, electrochemical equations, and mass and energy balances to develop relationships among the design and operating variables and the internal fuel cell stack conditions. The model produces the temperature, pressure and humidity profiles for the proposed stack as well as the amount of oxygen in the flow passage. The model is implemented on a spreadsheet which makes it easy to use and quick to change. An example of investigating the feasibility of converting Phosphoric Acid bi-polar plates to a Proton Exchange Membrane fuel cell is presented. The cell dimensions and operating conditions were provided to the model and the temperature variation was calculated. An inlet condition was then altered and the temperature variation recalculated. This was done to demonstrate the simplicity and usefulness of the model. It was concluded that the model is easy to implement and would be useful in the early stages of design development.