The report reviews the effect of surface area and thickness of fire loads in predicting the value of the heat release rate. The investigation arises from current Ph. D research at the University of Canterbury identifying the need for fire load data, which also includes the exposed surface area of the fuel items, so that the rate and duration of burning can be better assessed, especially during post-flashover fires. This is because at some stage of the fire, the fuel is no longer dependent on the ventilation characteristics but the surface area exposed to the fire. The investigation of the effect of surface and thickness on fire load is first carried out with the burning of single items, such as furniture normally found in each building occupancy. Later, fire load surveys on a range of typical building occupancies, such as university offices, motels and residential are conducted. Simple models for calculating the surface area of the fire load, especially for wood and plastic materials have been determined. Based on the methodology developed for the investigation, it is found that the larger the exposure of the fuel surface area to the fire, the higher the heat release rate, and the thicker the fuel, the longer the duration of burning. In other words, the value of the heat release rate is a function of the surface area, while the duration of burning is a function of the thickness of the fuel. Burning behaviour of the fire load inside a fire compartment during a post-flashover fire, based on the exposed surface to the fire is also presumed. Previous fire load surveys conducted are also included for comparisons of the results. Recommendations for future study of the effect of the surface area and thickness on fire loads during a fire are provided.